1 15 2 https://www.nal.usda.gov/exhibits/speccoll/files/original/1516419f8d411753953829faab4f24e5.pdf 8c8791b180b3fd5c1fda29c7cd2fddba PDF Text Text ItemDNunber °1045 Author Eisen, Seth Corporate Author Roport/Artldo TltlO TyPesci"iPt: The Vietnam Era Twin (VET) Registry: Method of Construction Journal/Book Title Year 000 ° Month/Day n Number of Images DOSCrlDtOn NOtBS 16 Alvin L - Young filed this item under "Vietnam Veterans Twin Study." Wednesday, July 11, 2001 Page 1846 of 1870 �The Vietnam Era Twin (VET) Registry: Method of Construction Seth Eisen, M.D. Research Service, St. Louis VA Medical Center, St. Louis, MO and Washington University School of Medicine William True, Ph.D. Psychiatry & Research Services St. Louis VA Medical Center, St. Louis, MO and St. Louis University School of Medicine Jack Goldberg Ph.D. University of Illinois, School of Public Health and Hines VA Cooperative Studies Coordinating Center, Hines, IL William Henderson, Ph.D. Hines VA Cooperative Studies Coordinating Center,Hines, IL C. Dennis Robinette, Ph.D. Medical Follow-up Agency, National Academy of SciencesNational Research Council, Washington, D.C. Work Performed at: Research Service, St. Louis VA Medical Center, St. Louis, MO; Cooperative Studies Program Coordinating Center, Hines VA Medical Center, Hines, IL; Medical Followup Agency, National Academy of Sciences-National Research Council, Washington, D.C. Acknowledgment of Funding: Cooperative Studies Program, Study #256, Veterans Administration Medical Research Service Correspondence: Seth Eisen, M.D. (151A-JB), St. Louis VA Medical Center, St. Louis, MO 63125, USA Running Title: VET Registry: Construction �VET Registry: Construction ABSTRACT A Vietnam Era (1964 - 1975) Twin Registry of American male-male veterans born between 1939 and 1955 has been developed to provide / a study sample for research evaluating the impact of Vietnam service on the medical and psychosocial aspects of health. In preparation for developing the Registry, several alternative sources of twins and methods for identifying twins were investigated. A computerized database of veterans discharged from the military after 1967 was selected as the source because it contains about fifty percent of the total Vietnam era veteran population, is reasonably unbiased, and provides a feasible method for identifying twins. Twins were identified using an algorithm which involved matching entries on the database for same last name, different first name, same date of birth, and similar social security number. Twin status was confirmed by review of military records. The registry, now complete, is composed of 7,400 twin pairs. It will be an important resource for future research projects. �VET Registry: Construction Key Words: Twins, Registries, Vietnam War, Veterans �VET Registry: Construction INTRODUCTION In the wake of America's reassessment of its attitudes towards the Vietnam War, persistent and increasing concern has developed t about possible long-term psychological and physical effects of the war on its servicemen.^ Consequently, the Veterans Administration (the government agency responsible for providing services to American veterans) has been encouraging research to clarify the relationship between Vietnam military service and current health. The Veterans Administration's Medical Research Service, Cooperative Studies Program has provided funds to perform the Vietnam Era Twin Study (VETS), a research project which will assess the long-term effects of the Vietnam experience on health by studying twin pairs where both siblings served in the military during the Vietnam era. The first step in the project was the development of a registry of Vietnam era twin pairs. paper describes the construction of this registry. The present A companion paper (5) examines the issue of bias in the registry. �VET Registry: Construction METHODS AND RESULTS Eligibility Criteria Eligibility criteria for entry into the, Vietnam Era Twin (VET) Registry are: male-male monozygotic and dizygotic twins born between 1939 and 1955 where both siblings served in the armed forces of the United States between 1964 and 1975. Approaches to the Ascertainment of Veteran Twin Pairs Two general approaches are available for identifying veteran twin pairs. The first starts with state based twin registries and attempts to determine whether the known twins on the state registries served on active duty during the Vietnam era. The second starts with computerized records of individuals with known military duty during the Vietnam era and attempts to identify twin pairs. Both approaches were piloted to determine the best method for constructing the VET Registry. 1. State Based Twin Registries Twin registries are maintained by several states in the United States. For example, the States of California, Virginia, and Connecticut have computerized registries of twins identified at birth using birth certificates (1,3). It is important to note that these registries do not continue to collect data on twins as they age. The process for identifying the subset of twins found on state registries who meet the VET Registry eligibility criteria was pilot tested with 55 twin pairs randomly selected from pairs born in the state of Connecticut during the years of �VET Registry: Construction interest. The selected pairs were matched against a comprehensive computer based list of discharged servicemen. list of discharged servicemen and their military records are located at the National Personnel Records Center (NPRC), St. Louis, Missouri. Because the NPRC contains 70 (including those of approximately nine million veterans), no uncommon names exist. The comprehensive million records Vietnam era The only relevant information coded on the computer file are names, social security or military service numbers, and military record location numbers. The matching of the 55 Connecticut twin names with the NPRC computer file produced thousands of potential twin pairs. Many names could be eliminated though, either because both twins were not listed or because the social security or military record location numbers excluded the particular names from military duty during the Vietnam era. typically matched pairs. Still, many names (sometimes hundreds) It was then necessary to obtain the stored military records and compare places of birth and parents names to determine whether a matched pair were in fact twins. 2. Computerized Records of Military Service The National Personnel Records Center (NPRC) To identify potential twin pairs using the NPRC location registry, a matching algorithm using two variables on the computerized data file (name and social security number) was developed. The social security number is a nine-digit �VET Registry: Construction identification number issued to every American wage earner as part of the national retirement system. The first three digits of the social security number indicate the state in which the application was made. The next two digits are encoded to reflect the year of application. It was assumed that twin siblings made application for their social security numbers in the same state, at the same social security office, and on approximately the same date. Therefore, the first three digits of the social security number would be the same for twins and the subsequent six digits would be very similar. The twin status of matched pairs was confirmed by review of military records located at the NPRC. The Bonus State Files Following the Vietnam War, the following states in the United States offered monetary awards to discharged veterans who served during the Vietnam era: Illinois, Indiana, Iowa, Minnesota, New Hampshire, North Dakota, Ohio, Pennsylvania, South Dakota, Vermont, and Wisconsin. Veterans applied to the state in which they lived for their Vietnam era service "bonus". states Many of the developed computerized application and disbursement records which can be used to identify potential twin pairs. While states varied in the data elements which were entered into the bonus files, and a social required was most contained name, sex, race, date of birth, security number. To identify twins from these files developing a computer matching algorithm. Twin status confirmed by reviewing military records at the NPRC. �VET Registry: Construction The Beneficiary Identification and Record Locator Subsystem (BIRLS) The BIRLS, a computerized listing of veterans who have filed for a benefit with the Veterans Administration, is maintained in a standard format and includes name, date of birth, race, and social security number (15). identified Potential twin pairs were by developing a computer matching algorithm similar to those previously described. Confirmation of twin status required examination of military records at the NPRC. The Defense Manpower Data Center (DMDC) The United States Department of Defense, at the Defense Manpower Data Center (DMDC), maintains a computer file of servicemen who were discharged from active military duty beginning in 1968. DMDC claims to have a complete listing of all discharges after 1972; between 1968 and 1972, the proportion of all discharges contained The in the DMDC computer files is unknown. The DMDC computer files contain between four and five million Vietnam era veterans (about fifty percent of all Vietnam era veterans) (14). Potential twin pairs were identified using a matching routine based on name, date of birth, and social security number. Confirmation of twin status was performed by military record review at the NPRC. Summary of Approaches of the Ascertainment of Veteran Twin Pairs A summary evaluation of possible sources of veteran twin pairs is presented in Table 1. Feasibility and bias are the two criteria 8 �VET Registry: Construction which form the basis for evaluation. Feasibility addresses the issue of whether it is possible to construct a large twin registry from a particular data source given the constraints of time and money. Bias addresses the issue of whether a systematic error in the ascertainment source might substantially compromise the subsequent utility of the VET Registry. (Insert Table 1 About Here) The major advantage of state twin registries is that they contain the universe of twin pairs born in a state during a specified time period and are therefore unlikely to be biased. However, since state registries usually contain a limited amount of information, determining whether both members of a pair served on active military duty during the Vietnam era is time consuming and expensive. Using the NPRC registry as a source of twins is also not feasible; the scant number of variables and the large number of veterans included on the registry precludes the development of a computer matching algorithm that has sufficient sensitivity. Both the Bonus State files and the BIRLS can be used to identify twin pairs at low cost. However, the potential for health related bias is large, since both members of a twin pair must have applied for a bonus or Veterans Administration benefit. The DMDC database permits rapid and low-cost identification of potential twin pairs. A known bias in this database is that it contains records for only those veterans who were discharged beginning in 1968. �VET Registry: Construction After carefully considering the advantages and disadvantages for constructing the twin registry from each of the above sources, the DMDC database was selected because it contains a '• r large proportion of the total Vietnam era population (about 50 percent), is reasonably unbiased, and is a feasible method for identifying twins. Final Method of Identifying Twin Pairs in the DMDC Database Only about 12 percent of pairs of DMDC registry members who had the same last name, different first names, same date of birth, and the same first three digits of the social security were demonstrated to be twins after review of their numbers military records. This twin identification rate was too small to be an economical method for construction of the VET Registry. Narrowing the criteria to include matching on the first five digits of the social security number, however, increased the proportion of possible pairs proven to be actual pairs to 50 percent. Therefore, this was the final matching criteria selected for construction of the Registry. The Registry is now complete. It contains 7,400 twin pairs. The addresses of Registry members are currently being obtained and a zygosity determination (13) and health survey questionnaire is being mailed. 10 �VET Registry: Construction DISCUSSION The present paper describes the construction of a new, large (7,400 pairs) twin registry which is based on military service during the Vietnam War era. The study of twins offers unique opportunities for understanding the role of genetic and environmental factors in a wide variety of normal biologic processes and diseases (6,11). The availability of registries of twins substantially facilitates the use of twins in research. Twin registries have been constructed using many different methods. These include all volunteer registries (for example, the Kaiser-Permanente registry) (4), disease focused registries (for example, the UCLA Registry for Genetic Studies in Autism) (12), registries where all members share a common, significant event (for example, the NAS-NRS Twin Registry of World War II veterans) (7), registries composed of a carefully constructed sample of a total population (for example, the registry developed from the National Health Examination Survey) (10), and national registries (for example, the Norwegian and Swedish registries) (2,9). The registry described in the present article is event focused, since it is based on male-male twins born between 1939 and 1955 where both members of each pair served in the armed forces of the United States during the Vietnam era. It was constructed from a computer data file provided by the Department of Defense, Defense Manpower Data Center, which contains a list 11 �VET Registry: Construction of servicemen discharged from active military duty beginning in 1968. The major advantages of the VET Registry are that it is t large and composed of a relatively young twin cohort who can be followed for many years. A detailed examination of ascertainment bias in the identification of twin pairs in the VET Registry is presented in a companion paper (5). It should be noted that Registry members are likely to be both physically and psychologically healthier then the general male population born between 1939 and 1955 (8). The NAS-NRC Twin Registry of World War II veterans is similar to the VET Registry. Both are composed of veteran twin pairs. The NAS-NRC Twin Registry was assembled by matching the names and dates of Caucasian multiple births between 1917 and 1927 provided by 42 state vital statistics offices with a VA master index which contained 99% of all World War II veterans. Twinship was confirmed by review of military records. About 16 r OOO twin pairs were identified (7). used This registry has been extensively to support diverse and important research projects. broaden the The VET Registry will supplement and substantially usefulness of the NAS-NRC Twin Registry. The VET Registry will be administered in a manner similar to the NAS-NRC Twin Registry. Access to the Registry will be overseen by the Committee on Epidemiology and Veterans Follow-up Studies, Division of Medical Sciences, National Academy of 12 �VET Registry: Construction Sciences-National Research Council. The Committee will review submitted proposals for scientific validity and encourage use of the Registry in a manner which insures long-term participation of the twins in research efforts. The first use of the Registry will be to support the VETS research project. It is expected that outside requests for access to the panel will be considered after 1989. 13 �VET Registry: Construction REFERENCES 1. California Bureau of Vital Statistics and Data Processing: Processing Procedures for Twin Study File. Unpublished document, March, 1984. 2. Cederlof R, Lorich U (1978): The Swedish Twin Registry. Prog Clin Biol Res 246(pt B):189-95. 3. Connecticut Division of Health Statistics: Multiple Birth Tape Layout. 4. Friedman GD, Lewis AM (1978): The Kaiser-Permanente Twin Registry. 5. Unpublished Document, October, 1980. Prog Clin Biol Res 24(pt B):173-7. Goldberg J, True Wm, Eisen S, Henderson Wm, and Robinette CD: The Vietnam Era Twin (VET) Registry: Ascertainment Bias. Acta Genet Med Gemellol (Roma), submitted. 6. Hrubec Z, Robinette CD (1984): The study of human twins in medical research. 7. N Engl J Med 310(7):435-41. Jablon S, Neel JV, Gershowitz H, Atkinson GF (1967): The NAS-NRC Twin Panel: methods of construction of the panel, zygosity, diagnosis, and proposed use. Am J Human Genet 19:133- 161. 8. Kendler KS, Holm NV (1985): Differential enrollment in twin registries: its effect on prevalence and concordance rates and estimates of genetic parameters. 34(3-4) :125-40. 14 Acta Genet Med Gemellol (Roma) �VET Registry: Construction 9. Kringlen E (1978): Norwegian twin registers. Prog Clin Biol Res 24(pt B):185-7. 10. McDowell AJ (1978): Twin Data Available from the National f Health Examination Surveys. 11. Nance WE (1984): The relevance of twin studies to cardiovascular research. 12. Prog Clin Biol Res 24(pt B):197-201. Prog Clin Biol Res 147:325-48. Ritvo ER, Freeman BJ, Mason Brothers A, Mo A, Ritvo AM (1985) : Concordance for the syndrome of autism in 40 pairs of afflicted twins. 13. Am J Psychiatry 142(1):74-7. Sarna S, Kaprio J, Sistonen P f Koskenvuo M (1978): Diagnosis of twin zygosity by mailed questionnaire. Hum Hered 28(4) :241-54. 14. United States Department of Defense, Defense Manpower Data Center: Data Base Profile and Overview. Unpublished document, October, 1982. 15. United States, Veterans Administration: Beneficiary Identification and Records Locator Subsystem. document, April, 1968. 15 Unpublished �VET Registry: Construction Table 1 - Potential Sources of Veteran Twin Pairs ASCERTAINMENT IMPLEMENTATION SOURCE BIASES FEASIBILITY State Twin time consuming and Registries costly National Per- time consuming and sonnel Records none likely costly none likely Center Registry Bonus State rapid and low cost Files biased toward veterans who requested a "bonus" from the state Beneficiary rapid and low cost biased toward VA benefit applicants Identification and Record Locator Subsystem (BIRLS) Defense Man- rapid and low cost biased towards power Data veterans discharged Center (DMDC) after 1968 16 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Alvin L. Young Collection on Agent Orange Description An account of the resource <p style="margin-top: -1em; line-height: 1.2em;">The Alvin L. Young Collection on Agent Orange comprises 120 linear feet and spans the late 1800s to 2005; however, the bulk of the coverage is from the 1960s to the 1980s and there are many undated items. The collection was donated to Special Collections of the National Agricultural Library in 1985 by Dr. Alvin L. Young (1942- ). Dr. Young developed the collection as he conducted extensive research on the military defoliant Agent Orange. The collection is in good condition and includes letters, memoranda, books, reports, press releases, journal and newspaper clippings, field logs and notebooks, newsletters, maps, booklets and pamphlets, photographs, memorabilia, and audiotapes of an interview with Dr. Young.</p> <p>For more about this collection, <a href="/exhibits/speccoll/exhibits/show/alvin-l--young-collection-on-a">view the Agent Orange Exhibit.</a></p> Text A resource consisting primarily of words for reading. Examples include books, letters, dissertations, poems, newspapers, articles, archives of mailing lists. Note that facsimiles or images of texts are still of the genre Text. Box The box containing the original item. 068 Folder The folder containing the original item. 1845 Series The series number of the original item. Series III Subseries III Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Creator An entity primarily responsible for making the resource Eisen, Seth William True Jack Goldberg William Henderson C. Dennis Robinette Title A name given to the resource Typescript: The Vietnam Era Twin (VET) Registry: Method of Construction Subject The topic of the resource Vietnam Experience Twin Study NPRC BIRLS DMDC ao_seriesIII https://www.nal.usda.gov/exhibits/speccoll/files/original/831290c6971ca2ec6a8b06b08dcea0f3.pdf 8e688da38c25fbfbc1ef0deb7f735230 PDF Text Text Item ID Number °1846 Author Goldberg, Jack Corporate Author Roport/Artlde Title Typescript: The Vietnam Era Twin (VET) Registry: Ascertainment Bias Journal/Book Title 0000 Month/Day Color Number of Images DeSGTipton NOtGS D 38 Alvin L Youn 9filed this item under "Vietnam Veterans Twin Study." Wednesday, July 11, 2001 Page 1847 of 1870 �The Vietnam Era Twin (VBT) Registry: Ascertainment Bias Jack Goldberg Ph.D. University of Illinois, School of Public Health and Mines VA Cooperative Studies Coordinating Center, Hines, IL William True, Ph.D. Psychiatry & Research Services St. Louis VA Medical Center, St. Louis, MO and St. Louis University School of Medicine Seth Eisen, M.D. Research Service, St. Louis VA Medical Center, St. Louis, MO and Washington University School of Medicine William Henderson, Ph.D. Hines VA Cooperative Studies Coordinating Center, Hines, IL C. Dennis Robinette, Ph.D. Medical Follow-up Agency, National Academy of SciencesNational Research Council, Washington, D.C. Work Performed at: Cooperative Studies Program Coordinating Center, Hines VA M e d i c a l Center, Hines, IL; Research Service, St. Louis VA Medical Center, St. Louis, MO; Medical Follow-up Agency, National Academy of Sciences-National Research Council, Washington, D.C. Acknowledgment of Funding: Cooperative Studies program, Study #256, Veterans Administration Medical Research Service Correspondence: Jack Goldberg, Ph.D., Study Epidemiologist, Vietnam Era Twin Study, Hines VA CSPCC (151JO, Hines, IL 60141 USA Running Title: VET Registry: Ascertainment Bias 1 �VET Registry: Ascertainment Bias ABSTRACT An examination of ascertainment bias in the identification of twin pairs in the Vietnam Era Twin Registry has been conducted. A complete listing of all male-male Vietnam era veteran twin pairs born in Connecticut between 1939 and 1955 was obtained (n=150). An attempt was made to match these pairs with a listing of Vietnam era veteran twin pairs derived from the United States Department of Defense's Defense Manpower Data Center (DMDC) computer files. The results indicate that the DMDC files identified only 46.7% of the 150 Connecticut born Vietnam era veteran pairs. Statistically significant differences (p<.05) between pairs found on the DMDC files and Connecticut veteran pairs missing from the DMDC files are observed for the following variables: a) year of discharge from military service, b) total length of active military service, c) branch of service, and d) foreign service. No consistent pattern of bias is observed for factors related to the physical and psychosocial health of veteran pairs. The implications of the ascertainment biases in the Vietnam Era Twin Registry are discussed. �VET Registry: Ascertainment Bias Key Words: Twin registers, Vietnam veterans, Bias, Military service �VET Registry: Ascertainment Bias INTRODUCTION Veterans have claimed that service in Vietnam during the Vietnam War is associated with a wide variety of psychological and physiological illnesses (3,5,7,12). For example, exposure to combat in the war theater may cause Post-Traumatic Disorder (PTSD) (2). Stress Other features of the war having potential long-term effects include exposure to chemicals, diseases endemic to Southeast Asia, and certain medications and illicit drugs (8). In spite of considerable effort to define the relationship between the Vietnam experience and adverse health effects, few well-designed studies exist. To a large extent, this reflects the problems involved with defining a group of veterans who can serve as an adequate non-Vietnam experienced control population. The Vietnam Era Twin Study (VETS) has been suggested as a method for minimizing this problem. In brief, the VETS will assess the effects of the Vietnam experience on health by studying twin pairs concordant on military service but discordant on service in Vietnam. Thus, maximum control of non-Vietnam related hereditary and environmental factors is obtained, since monozygotic twins are genetically identical and monozygotic and dizygotic twins share more common environmental experiences than any other pair of individuals. The first step in the project was the development of a registry of Vietnam era twin pairs. In a companion paper, the rationale and method of construction of the Vietnam Era Twin 4 �VET Registry: Ascertainment Bias (VET) Registry are discussed (6); the purpose of this paper is to evaluate the potential for bias in the Registry. �VET Registry: Ascertainment Bias METHODS AND MATERIALS The examination of ascertainment bias in the VET Registry first required an unbiased source of veteran twin pairs. This unbiased source was provided by the State of Connecticut twin register (1). Based on an exhaustive manual search of hard copy military records at the National Personnel Records Center (NPRC) (6) veteran twin pairs born in Connecticut between 1939 and 1955 were identified (10,11). The completeness of the VET Registry is easily accomplished by attempting to link the veteran twin pairs identified using the Defense Manpower Data Center (DMDC) (9) database (the source of the VET Registry) with veteran twin pairs derived from the Connecticut twin register. Linkage is based on an exact match for social security number and date of birth; matched names were confirmed by manual review. The proportion of all Connecticut born veteran twins found on the DMDC database describes the completeness of VET Register ascertainment. The next step in assessing bias in the VET Registry involved comparing Connecticut born veteran twins found on the DMDC database and those not found on the DMDC database. It is thereby possible to determine if the veteran pairs ascertained via the DMDC database are any different than the veteran pairs missing from the DMDC database. The variables used to compare the groups are derived from two sources: a) the military service record and b) a twenty-four page questionnaire which is administered to all veteran twin pairs as part of the VETS. The variables obtained �VET Registry: Ascertainment Bias from the service record are shown in Table 1; those obtained from the questionnaire are shown in Table 2. (Insert Tables 1 and 2 about here) The statistical analysis presents the data in unpaired form for simplicity. Since the paired analysis of these data show no difference from the unpaired analysis only the unpaired analysis is presented. Hypothesis testing is done using the chi-squared statistic for categorical data except where indicated. For continuously distributed data the t-test is used for hypothesis testing. �VET Registry: Ascertainment Bias RESULTS Completeness of the Vietnam Era Twin Registry A microdata tape transcript of the Connecticut twin register was obtained. This register contained 1,544 male-male twin pairs born between 1939 and 1955. Based on a manual search of hard copy military records at NPRC it was determined that 150 Connecticut born pairs both served on active military duty during the Vietnam era; for these 150 pairs social security numbers were ascertained from the military records. A listing of 15,711 potential veteran twin pairs from the DMDC was also obtained; these potential twins were identified using a matching algorithm based on: a) same last name, different first name, b) same date of birth, and c) same first five digits of the social security number (6). Using the social security number and date of birth an attempt was made to link the 150 Connecticut born veteran twins with the DMDC file of 15,711 potential veteran twin pairs. The record linkage identified 70 pairs that appeared on both files. Thus, the DMDC file contains approximately half (46.7%) of the total number of Vietnam era veteran twin pairs born in Connecticut. It was therefore important to evaluate the VET Register for possible ascertainment bias. Demographic Factors Table 3 presents the distribution of the demographic factors: age, race, education at enlistment, and marital status at 8 �VET Registry: Ascertainment Bias enlistment by DMDC status. Of the demographic factors examined, race demonstrated a marginally significant difference between the two DMDC groups. The non-DMDC group contains a smaller percentage of non-whites compared to the DMDC group (though this difference is difficult to evaluate due to the small number of non-whites). (Insert Table 3 about here) Enlistment Examination Factors Table 4 presents the enlistment examination factors by DMDC status. Both systolic and diastolic blood pressure are measured during the enlistment physical examination. The Department of Defense classifies fitness for military duty on six dimensions: physical, upper extremities, lower extremities, hearing, vision, and neuropsychiatric. For each dimension a rating of 1 (no limitations) to 4 (unfit for duty) is assigned. These six variables have been dichotomized into no limitations versus any limitations. An examination of the enlistment examination factors shows that there are no significant differences between individuals on the DMDC compared to individuals not on the DMDC. (Insert Table 4 about here) Military Service Factors Military service factors (Table 5) are strongly related to the presence of an individual on the DMDC. The mean year of discharge for individuals that appear on the DMDC (x^ = 1971) is �VET Registry: Ascertainment Bias significantly later that the mean year of discharge for individuals who do not appear on DMDC Cx"2 » 1969). Likewise, mean year of enlistment is significantly later in the DMDC group CXi = 1968) compared to the non-DMDC group ("x"2 « 1966). Somewhat more surprising is the significant difference in the mean length of military service; the DMDC group served longer (x^ •> 1,175 days) compared to the non-DMDC group (x^ = 1,027 days). of service is strongly associated with DMDC status. Branch Those individuals who appeared on the DMDC, by comparison with those who did not appear on the DMDC, were more likely to be Navy (33.6 vs 23.1) or Air Force (19.3 vs 10.6) personnel. Lastly, the percent of foreign service was significantly greater for men who appeared on the DMDC (87.0) compared to those who did not (66.0). (Insert Table 5 about here) Vietnam Experience Factors Table 6 presents the distribution of Vietnam experience factors by DMDC status. No significant differences were observed for the percent who served in Vietnam or the mean length of service in Vietnam by DMDC group. However, a marginally significant association exists between the mean year of first rotation through Vietnam and DMDC group, with the DMDC group entering Vietnam an average of one year later than the non-DMDC group. The specific combat roles/experiences are worthy of special discussion. Eighteen specific combat roles/experiences were developed with the assistance of expert consultants in the area 10 �VET Registry: Ascertainment Bias of war stress. The respondent was asked to indicate whether he had experienced a particular combat role/experience while serving in Vietnam. The combat index is created by taking the sum of all positive responses to the 18 combat role/experience questions. The results indicate that four combat role/experiences exhibit an association with DMDC status. For the combat role/experiences of firing an artillery on enemy and receiving incoming fire, sharp differences exist between DMDC and non-DMDC veterans. Nearly 20% of the veterans not found on the DMDC fired artillery on the enemy compared to 2.1% of the veterans found on DMDC; and 80% of the non-DMDC veterans received incoming fire compared to 56.3% of DMDC veterans. Veterans not found on the DMDC are also more likely to have served on a river patrol and engaged the enemy in a firefight. While only four of the combat roles/experiences exhibited at least marginally significant differences, a general pattern of increased combat exposure in the non-DMDC group compared to the DMDC group is displayed in 14 of the 18 possible combat roles/experiences. However, the mean combat intensity index was not significantly greater in the non-DMDC group compared to the DMDC group. (Insert Table 6 about here) Physical Health Factors Table 7 presents the distribution of the physical health factors by DMDC status. Each of 15 physical health questions were asked in the form: "Since active military duty 1965 - 1975, have you 11 �VET Registry: Ascertainment Bias had this problem?" Only the prevalence of nerve disorders demonstrated a statistically significant association with DMDC status; a greater proportion of men found on the DMDC database reported nerve disorders compared to men not found on the DMDC database. It is interesting to note that no trend of increased or decreased prevalence of physical health factors is associated with DMDC status. Of the 15 conditions examined, seven had an increased prevalence associated with the DMDC database while eight had decreased (or no difference) in prevalence associated with DMDC database. (Insert Table 7 about here) Health Habit Factors Table 8 presents the relationship between health habits and DMDC status. No significant differences were observed between the two DMDC groups and the following variables: current smoking status, mean number of cigarettes smoked per day, current alcohol drinking status, and mean number of alcoholic drinks per week. (Insert Table 8 about here) Psychosocial Health Factors The relationship between psychosocial health factors and DMDC status is presented in Table 9. Fifteen indicators of the PTSD, derived from the American Psychiatric Association's most recent revision of the Diagnostic and Statistical Manual (DSM-III) are included in the survey. (12), Veterans were asked to rank the frequency of occurrence of each symptom during the preceding six 12 �VET Registry: Ascertainment Bias months on a five-point scale from very often to never. Only one of the fifteen indicators of PTSD symptomatology, trouble concentrating, demonstrated a significant association with DMDC status. Individuals on the DMDC database reported a statistically significant lower frequency of difficulty concentrating by comparison with individuals not found on the DMDC database. The final psychosocial health factor examined was whether servicemen had sought professional help for emotional problems following discharge. No significant association with DMDC status was demonstrated. (Insert Table 9 about here) 13 �VET Registry: Ascertainment Bias DISCUSSION The preceding analysis demonstrates that the VET Registry contains about half of the total cohort of twin pairs who meet the eligibility criteria for inclusion. By comparison with all veteran twin pairs, the Registry is biased in terms of certain aspects of military service but not in terms of the physical and psychosocial variables of importance to the VETS. Pairs found on DMDC are more likely to have served at a later period during the Vietnam era and to have had their first rotation in Vietnam at a later date. These results are expected, based on our knowledge of when the DMDC database was developed (6). Somewhat more difficult to explain are the DMDC biases toward a longer length of active duty service, a greater proportion of Navy and Air Force personnel, a greater proportion of foreign service, and a possibly lower combat exposure. One explanation of these biases might be that individuals in the Navy and Air Force typically serve longer tours of duty (4 years) and are less likely to be combat exposed. For example, an Army draftee who served two years beginning in 1965 would not appear in the DMDC database, since the DMDC began collecting data with men discharged in 1968; conversely, a Navy enlisted man who served aboard a ship off the coast of Vietnam for four years (beginning in 1965) would appear in the DMDC database. A second possible explanation is that the quality of discharge data submitted to DMDC headquarters varied by the branch of service. 14 �VET Registry: Ascertainment Bias If the Marines and Army submitted data that had a greater number of errors in the spelling of last name, dates of birth or social security numbers by comparison with Navy and Air Force data, then fewer potential Army and Marine twins would be identified by the matching algorithm. The observed biases in duration of service, foreign service and combat exposure would result. In contrast to the several biases in the DMDC database related to the military service experience, relatively few biases were observed for the variables that pertained to physical and psychosocial health. It is possible that the rarity of many specific health outcomes made it unlikely to detect differences between the DMDC and non-DMDC groups. However, the great similarity between the DMDC and non-DMDC groups for variables such as alcohol consumption, marital status, cigarette smoking, physical health, and psychosocial health suggest that major biases are not present. In summary, there is no reason to believe that the observed military service biases in the DMDC data tapes will substantially affect the validity of the analyses of the physical and psychosocial variables of twin pairs identified using the DMDC data files. 15 �VET Registry: Ascertainment Bias REFERENCES 1. American Psychiatric Association: Diagnostic and Statistical Manual of Mental Disorders III (DSM III). Washington, DC; 1980. 2. Boulanger G, Kadushin C (1986): The Vietnam Veteran Redefined: Fact and Fiction. Hillsdale, NJ: Lawrence Erlbaum Associates. 3. card J (1983): Lives after Vietnam. Lexington, MA D.C. Heath 4. Connecticut Division of Health Statistics: Multiple Birth Tape Layout. 5. Unpublished document, October, 1980. Egendorf A, Kadushin C, Laufer RS, Rothbart G, & Sloan L (1981): Legacies of Vietnam Vol. 1 Summary of findings. Washington, DC: US Government Printing Office. 6. Eisen S, True Wm, Goldberg J, Henderson Wm: The Vietnam Era Twin (VET) Registry: Method of Construction of a New Twin Panel. Acta Genet Med Gemellol (Roma), submitted. 7. Harris L (1980): Myths and realities: A study of attitudes toward Vietnam era veterans. Washington, DC: Veterans Administration, Senate Committee. 8. Sonnenberg SM, Blank AS Jr, Talbott JA (1985): The Trauma of War: Stress and Recovery in Viet Nam Veterans. Washington, DC: American Psychiatric Press, inc. 9. United States Department of Defense, Defense Manpower Data Center: Data Base profile and Overview. October, 1982. 16 Unpublished document, �VET Registry: Ascertainment Bias 10. United States, National Archives and Records Service, National Personnel and Records Center: Directory of Military Personnel and Related Records. Unpublished document, September, 1974. 11. United States, National Archives and Records Service, National Personnel Records Center: Administrative History of the National Personnel Records Center. Unpublished document, December, 1981. 12. Veterans Administration, Reports and Statistics Service, Office of the Controller, 1979 National Survey of Veterans II, Summary Report, 1980. 17 �VET R e g i s t r y : A s c e r t a i n m e n t Bias Table 1. Variables Obtained From the Military Service Record Demographic Factors Age Race Education at Enlistment Marital Status at Enlistment Enlistment Examination Factors Blood Pressure Fitness for Military Duty Military Service Variables Branch Year of Enlistment Year of Discharge Length of Service Foreign Service 18 �VET Registry: Ascertainment Bias Table 2. Variables Obtained From the Survey Vietnam Experience Factors Service in Vietnam Year First Sent to Vietnam Length of Service in Vietnam Fired Artillery on Enemy Flew in Aircraft Flew in Helicopter Stationed at Forward Observation Post Served as a Tunnel Rat Served on a River Patrol Field Demolitions Expert Retrieved Dead Bodies From Field Served as a Medic in Combat Received Incoming Fire Encountered Mines and Booby Traps Received Sniper or Sapper Fire Unit Patrol Ambushed Aircraft Shot Down Engaged Enemy in Firefight Saw Soldiers Killed Wounded Captured by the Enemy 19 �VET Registry: Ascertainment Bias Table 2. Variables Obtained From the Survey (continued) Combat Exposure Index Physical Health Factors Hypertension Respiratory Condition Cancer Heart Disease Stroke Kidney Problems Skin Disorders Diabetes Stomach Disorders Liver Disorders Blood Disorders Nerve Disorders Joint Disorders Hearing Problems Other Health Problems 20 �VET Registry: Ascertainment Bias Table 2. Variables Obtained From the Survey (continued) Health Habits Factors Current Smoking Status Total Pack Years of Smoking Current Alcohol Drinking Status Number of Alcoholic Drinks Consumed Per Week Psychosocial Health Factors Trouble Sleeping Dreams or Nightmares About Military Service Painful Memories About Military Service Avoided Activities That Brought Back Memories of Military Service Experienced Flashbacks Strong Feelings About Military Memories Felt Guilt About Actions In The Military Had Trouble Concentrating Had Trouble With Memory Irritable and Short-Tempered Angry or Agressive Behavior Lost Interest in Usual Daily Activities Felt Distant From Everyone 21 �VET Registry: Ascertainment Bias Table 2. Variables Obtained From the Survey (continued) Felt Life is Not Meaningful Easily Startled or on Guard All The Time Sought Help For Emotional Problems After Discharge 22 �VET R e g i s t r y : A s c e r t a i n m e n t Bias Table 3. DMDC Status by the Demographic Factors Found on DMDC Mean Education Grade 97.5 (n=138) White (%) (n=159) 92.8 Race* 20 (n=139) Mean Age at Enlistment on DMDC 20 Demographic Factors Not Found (n-160) 12 (n*139) Single (%) *p<.10 by Fisher's Exact Test 23 94.7 (n=138) Martial Status at Enlistment (n=154) 98.6 at Enlistment 12 (n-151) �VET R e g i s t r y : A s c e r b a i n m e n t Table 4. DMDC Status by the Enlistment Examination Factors Found Enlistment Examination Factors Not Found on DMDC on DMDC Mean Systolic Blood Pressure 124 124 (n=119) 73 75 (n=119) (n-146) 0.8 0.7 (n-128) (n-150) 1.6 .7 (n=128) (n-150) 3.9 2.0 Mean Diastolic Blood Pressure Fitness for Military Duty Physical Limitations (%) Upper Extremities Limitations (%) Lower Extremities Limitations (%) (n-150) 24 Bias �VET R e g i s t r y : A s c e r t a i n m e n t Bias Table 4. DMDC Status by the Enlistment Examination Factors .(Continued) Found Not Found on DMDC on DMDC Hearing - Limitations (%) 2.3 2.7 (n=*128) (n»150) » Visual - Limitations (%) 34.4 32.0 (n=150) Neuropsychiatric - Limitations (%) 0.0 25 0.0 �VET R e g i s t r y : A s c e r t a i n m e n t Bias Table 5. DMDC Status by Military Service Factors Found Not Found Military Service Factors on DMDC on DMDC Mean Year of Discharge* 1971 1969 (n=139) (n-158) Mean Year of Enlistment* 1968 1966 (n-139) (n-159) 1,175 1,027 (n=139) (n-158) Mean Length of Active Duty Service in days* Branch* Army (%) 45.0 56.3 Navy (%) 33.6 23.1 2.1 10.0 19.3 10.6 Marines (%) Air Force (%) (n-140) 26 (n-160) �VET R e g i s t r y : A s c e r t a i n m e n t Bias Table 5. DMDC Status by Military Service Factors . (Continued) Found on DMDC Foreign Service ( ) %* Not Found on DMDC 87.0 66.0 (n=138) (n=156) *p<.001 27 �VET R e g i s t r y : A s c e r t a i n m e n t Bias Table 6. DMDC Status by Vietnam Experience Factors Found Vietnam Experience Factors Vietnam Service (%) Not Found on DMDC on DMDC 40.3 (n="119) 30.8 (n-133) Mean Year of First Service in Vietnam*** 1969 1968 (n=48) (n-41) 327 343 (n-43) (n=36) 2.1 19.5 (n=47) (n-41) 14.6 12.2 (n=48) (n=41) 14.6 22.0 (n=48) (n-41) Mean Length of Vietnam Service in days Fired Artillery on Enemy* (%) Flew in Aircraft (%) Flew in Helicopter (%) 28 �VET R e g i s t r y : A s c e r t a i n m e n t Bias Table 6. DMDC Status by Vietnam Experience Factors '(Continued) Found on DMDC Vietnam Experience Factors Not Found on DMDC Stationed at a Forward Observation Post (%) 16.7 (n=48) (n-41) 4.2 Served as a Tunnel Rat (%) 19.5 4.9 (n-41) Served as a River Patrol ** (%) 0.0 7.3 (n=48) 8.3 5.0 (n=48) Field Demolitions Expert (%) (n=40) 0.0 4.9 Retrieved Dead Bodies From Field (%) (n=48) Served as a Medic in Combat (%) 2.1 2.4 (n=48) (n-41) 29 �VET R e g i s t r y : A s c e r t a i n m e n t Bias Table 6. DMDC Status by Vietnam Experience Factors .(Continued) Found Vietnam Experience Factors Not Found on DMDC on DMDC 27.1 29.3 Wounded (%) (n=48) Captured by Enemy (%) 2.1 (n-41) 0.0 (n=48) Mean Combat Exposure Index 3.2 (n=48) *p<.05 by Fisher's Exact Test **p<.10 by Fisher's Exact Test ***p<.10 by Unpaired t-test Test 31 4.3 �VET R e g i s t r y : A s c e r t a i n m e n t Bias Table 7. DMDC Status by the Physical Health Factors Found on DMDC on DMDC 16.4 Physical Health Factors Not Found 15.5 Hypertension (%) (n-116) Respiratory Condition (%) 6.9 (n-116) Cancer (%) 0.0 (n=116) Heart Disease (%) . 1.7 (n-116) Stroke (%) 0.0 (n-129) 10.9 (n-129) 0.0 (n»128) 3.1 (n-129) 0.0 (n»129) Kidney Problems (%) 8.6 (n-116) Skin Disorder (%) 12.9 (n-116) 32 5.4 (n-129) 11.0 (n-127) �VET R e g i s t r y : A s c e r t a i n m e n t Bias Table 7. DMDC Status by the Physical Health Factors .(Continued) Found Physical Health Factors Not Found on DMDC on DMDC Diabetes (%) 0.0 2.3 <n-129) Stomach Disorders ( ) % 15.5 15.5 (n=116) <n-129) Liver Disorders 2.6 (n-116) Blood Disorders 0.9 3.9 (n-129) 2.3 (n-129) Nerve Disorders* (%) 12.9 (n-116) Joint Disorder (%) 12.7 (n=118) 33 3.9 (n-129) 12.4 (n-129) �VET R e g i s t r y : Ascertainment Bias Table 7. DMDC Status by the Physical Health Factors (Continued) Found Physical Health Factors Hearing Problem (%) Not Found on DMDC on DMDC 16.2 (n-117) Other Health Problems ( ) % 28.4 (n-102) *p=.01 by Fisher's Exact Test 34 14.6 (n-130) 24.3 (n=107) �VET R e g i s t r y : A s c e r t a i n m e n t Bias Table 8. DMDC Status by the Health Habits Factors Found Not Found Health Habits Factors on DMDC on DMDC Currently Smoking (%) 37.9 45.0 (n=116) (n-132) Mean Number of Cigarettes 26 Per Day Among Smokers (n=80) 27 (n=101) Currently Drinks Alcoholic 89.6 82.7 (n-115) Beverages (%) (n-127) Mean Number of Alcoholic Beverages Consumed Per Week Among Drinkers 17 16 (n=103) 35 �VET R e g i s t r y : A s c e r t a i n m e n t Bias Table 9. DMDC Status by The Psychosocial Health Factors Found Psychosocial Health Factors Not Found on DMDC on DMDC Mean Value for Trouble Sleeping 3.5 3.6 (n-117) (n-132) 4.5 4.5 (n-119) (n-132) 4.4 4.5 (n=119) (n-132) Mean Value for Dreams or Nightmares about Military Service Mean Value for Painful Memories about Military Service Mean Value for Avoided Activities that Brought Back Memories of Military Service 4.5 (n-118) 4.5 (n-132) Mean Value for Experienced Flashbacks 4.6 (n-119) 36 4.4 (n-132) �VET R e g i s t r y : A s c e r t a i n m e n t Bias Table 9. DMDC Status by The Psychosocial Health Factors (Continued) Found Psychosocial Health Factors Not Found on DMDC on DMDC Mean Value for Strong Feelings about Military Memories 4.3 (n-119) 4.4 (n-132) Mean Value for Felt Guilt About Actions in the Military 4.3 (n-119) 4.4 (n-132) Mean Value for Trouble* Concentrating 4.1 (n-119) 4.4 (n-132) Mean Value for Trouble With Memory 4.1 (n-119) 4.3 (n-132) Mean Value for Being Irritable or Short-Tempered 3.7 (n-119) 37 3.8 (n-132) �•I k VET R e g i s t r y : A s c e r t a i n m e n t Bias Table 9. DMDC Status by The Psychosoclal Health Factors (Continued) Found Psychosoclal Health Factors Not Found on DMDC on DMDC Mean Value for Angry or Aggressive Behavior 4.1 (n-118) 4.1 (n-132) Mean Value for Lost Interest In Usual Daily Activities A.I (n-119) 4.2 (n-132) Mean Value for Felt Distant From Everyone 4.1 (n-119) 4.2 (n-132) Mean Value for Life is Not Meaningful 4.5 4.4 (n-132) 38 �V < VET R e g i s t r y : A s c e r t a i n m e n t Bias Table 9. DMDC Status by The Psychosocial Health Factors (Continued) Found Psychosocial Health Factors Not Found on DMDC on DMDC Mean Value for Easily Startled or on Guard All The Time 4.2 (n=119) 4.3 (n=132) Sought Help for Emotional Problems After Discharge (%) 17.7 (n-119) *p<.05 39 21.2 (n=132) � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Alvin L. Young Collection on Agent Orange Description An account of the resource <p style="margin-top: -1em; line-height: 1.2em;">The Alvin L. Young Collection on Agent Orange comprises 120 linear feet and spans the late 1800s to 2005; however, the bulk of the coverage is from the 1960s to the 1980s and there are many undated items. The collection was donated to Special Collections of the National Agricultural Library in 1985 by Dr. Alvin L. Young (1942- ). Dr. Young developed the collection as he conducted extensive research on the military defoliant Agent Orange. The collection is in good condition and includes letters, memoranda, books, reports, press releases, journal and newspaper clippings, field logs and notebooks, newsletters, maps, booklets and pamphlets, photographs, memorabilia, and audiotapes of an interview with Dr. Young.</p> <p>For more about this collection, <a href="/exhibits/speccoll/exhibits/show/alvin-l--young-collection-on-a">view the Agent Orange Exhibit.</a></p> Text A resource consisting primarily of words for reading. Examples include books, letters, dissertations, poems, newspapers, articles, archives of mailing lists. Note that facsimiles or images of texts are still of the genre Text. Box The box containing the original item. 068 Folder The folder containing the original item. 1846 Series The series number of the original item. Series III Subseries III Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Creator An entity primarily responsible for making the resource Goldberg, Jack William True Seth Eisen William Henderson C. Dennis Robinette Title A name given to the resource Typescript: The Vietnam Era Twin (VET) Registry: Ascertainment Bias Subject The topic of the resource Vietnam Experience Twin Study DMDC NPRC ao_seriesIII