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Mortality of Veteran Participants in the CROSSROADS Nuclear Test (1996)

Chapter:Characterization of the Cohorts and Analysis Plan

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Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×

10
Characterization of the Cohorts and Analysis Plan

The overall goal of the analysis is to compare mortality among CROSSROADS participants with that among controls. In this chapter, we first describe the nature of the data on which that analysis rests and then describe the multivariate analysis plan itself. In an earlier chapter we presented data from the study, since some of the analytic strategies are influenced by our knowledge of our data's quality and idiosyncrasies. Data-based findings relating to the multivariate exposure-outcome relationships are presented in the following chapter (Chapter 11).

We have described in earlier chapters the detailed data collection plans and the practical adjustments that were necessary during their implementation. Refer to Chapter 5 for information on data sources. Chapters 6 and 7 describe who is in the analysis, while Chapters 8 and 9 discuss what data items are used and in what manner.

Data Decisions Taken Before Analysis

Restricting Data Elements or Sample Definition

In the overall attempt to balance the validity, precision, understandability, and usefulness of the analyses in this report, we made the following decisions, based mostly on issues of data availability:

Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×
  • Use the 1994 participant database provided by the Defense Nuclear Agency (DNA). (See Appendix E for a detailed description of procedures undertaken to validate the completeness of the participant roster.)
  • Restrict analyses to Navy participants and controls (see Chapter 6).
  • Do not include in participant cohort those individuals who came on duty in the CROSSROADS area of operations after the officially designated period of the operation (see Chapter 6).
  • Exclude from the control cohort those also in the participant cohort (see Chapter 6).
  • Include participants and controls who have other-than-CROSSROADS nuclear test participation (see Chapter 6).
  • Use male mortality rates, since the control cohort is almost totally male (gender generally was not recorded on the research files for participants), when making comparisons to standard populations (e.g., the U.S. population for specific years). However, do not exclude female military personnel from the participant or control study cohorts.
  • Do not use dosimetry; use exposure surrogate variables (see Chapter 8).

Data Cleaning and Variable Development

  • Code vital status outcome as a dichotomy: "Known Dead" and "Not Known to be Dead." The latter included participants and controls known to be alive, having date of death after prearranged study cut-off (31 December 1992), and others for whom no death confirmation was obtained through the Department of Veterans Affairs (VA), who were presumed to be alive (see Chapter 9).
  • For VA claims folders that did not contain a date of death from VA records or an acquired death certificate and that had been transferred from VA to a Federal Archives Record Center (FARC), use date of folder transfer to calculate an estimated date of death (see Chapter 9).
  • Because military records used only two digits to designate year of birth, assign a century-of-birth prefix of "l9" to years of birth 00 to 30 and the prefix "18" to years 31 to 99.
  • Create a "boarder" variable to include participants assigned in the appropriate time period to one or more units known to be a target ship, a radiation safety unit, or a boarding team (see Chapter 8).
  • Consolidate occupational specialty information into a two-level analysis variable (Engineering & Hull enlisted, other enlisted) to capture hypothesized exposure differences (see Chapter 8).
  • Because of small numbers (paygrade and rank) or unavailable information (occupation), consider all officers as one category.
Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×

Univariate Descriptions of Study Population

As we describe later in this chapter, we base our inferential comparisons on data adjusted for confounding influences on exposure-mortality relationships. Here, we present univariate (unadjusted) descriptive statistics on the variables used in later models. This information supports our belief that the Navy participant and control cohorts are similar in characteristics we can measure. Tables 10-1 through 10-3 show the numerical balance between participant and control cohorts for age, rank (or rating), and occupational specialty, respectively, for Navy personnel.

TABLE 10-1. Age-at-Shot Distribution of Navy Participants and Controls

 

 

Participant Cohort

Control Cohort

Agea

Years in Interval

No.

%

No.

%

≥ 16 and < 21

5

23,081

59.7

19,511

55.7

≥ 21 and < 26

5

9,504

24.6

9,365

26.7

≥ 26 and < 36

10

4,730

12.2

5,053

14.4

≥ 36 and < 46

10

1,134

2.9

962

2.7

≥ 46 and < 56

10

179

0.5

134

0.4

≥ 56 and < 66

10

11

0.0

2

0.0

≥ 66

2

2

0.0

1

0.0

Missing

 

27

0.1

8

0.0

Totalb

 

38,668

100

35,036

100

a See Chapter 9 for discussion of the age variable.

b Mean age-at-shot for Navy participants is 22.06 years; for controls, 22.50.

Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×

TABLE 10-2. Distribution of Ranks and Ratings Among Navy Participants and Controls

 

Participant Cohort

Control Cohort

Paygrade*

No.

%

No.

%

E1 Junior Enlisted

12

0.0

10

0.0

E2 Junior Enlisted

10,624

27.5

9,773

27.9

E3 Junior Enlisted

7,321

18.9

6,616

18.9

E4 Midlevel Enlisted

5,377

13.9

4,881

13.9

E5 Midlevel Enlisted

4,917

12.7

4,225

12.1

E6 Senior Enlisted

4,316

11.2

3,752

10.7

E7 Senior Enlisted

2,718

7.0

2,330

6.7

W1 (Warrant) Officer

70

0.2

0

W2 (Warrant) Officer

425

1.1

477

1.4

W3 (Warrant) Officer

1

0.0

0

W4 (Warrant) Officer

1

0.0

0

O1 (Commissioned) Officer

934

2.4

1,186

3.4

O2 (Commissioned) Officer

719

1.9

786

2.2

O3 (Commissioned) Officer

526

1.4

491

1.4

O4 (Commissioned) Officer

338

0.9

259

0.7

O5 (Commissioned) Officer

194

0.5

167

0.5

O6 (Commissioned) Officer

157

0.4

74

0.2

O7 (Commissioned) Officer

0

0

O8 (Commissioned) Officer

10

0.0

1

0.0

O9 (Commissioned) Officer

4

0.0

0

O10 (Commissioned) Officer

2

0.0

0

Missing

2

0.0

8

0.0

Total

38,668

100

35,036

100

* See Chapter 8 for description of paygrade, rank, and rate.

Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×

TABLE 10-3. Distribution of Occupational Specialties Among Navy Participants and Controls

 

Participant Cohort

Control Cohort

Occupation*

No.

%

No.

%

Administrative and clerical

5,248

13.6

4,531

12.9

Aviation

920

2.4

519

1.5

Construction

322

0.8

285

0.8

Deck

2,444

6.3

2,204

6.3

Dental

1

0.0

0

Electronics

415

1.1

382

1.1

Engineering & Hull

9,399

24.3

8,756

25.0

Medical

639

1.7

582

1.7

Miscellaneous

459

1.2

401

1.1

Ordnance

1,455

3.8

1,343

3.8

Precision equipment

4

0.0

3

0.0

Seaman

13,776

35.6

12,481

35.6

Steward

213

0.6

101

0.3

Unknown

3,371

8.7

3,428

9.8

Missing

2

0.0

20

0.1

Total

38,668

100

35,036

100

* See Chapter 8 for description of Navy occupational specialties.

Participants are labeled as Nonboarding and Boarding and are present in the cohorts in numbers shown in Table 10-4.

TABLE 10-4. Distribution of Boarders in the Study Cohort

 

Participant Cohort

Control Cohort

Boarder*

No.

%

No.

%

Yes

8,996

23.3

0

0

No

29,672

76.7

35,036

100

Total (participants only)

38,668

100

35,036

100

* See Chapter 8 for discussion of boarder variable.

Missing Data

Imputation of Fact and Date of Death

Because we classified approximately 500 individuals as "Dead" solely because their VA claims folder had been transferred to a Federal Archive Records Center (FARC), we devised a test to determine whether such imputation of fact and date of death was justifiable. Looking at records with both noted dates of death and FARC transfer dates, we determined that there is a

Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×

definite relationship between year of death and the date a claims folder is transferred to a FARC. We used the year-specific lag time for those known pairs to impute a lag time for date of death for those with only the FARC transfer date. For records transferred between 1956 and 1962, we adjusted the date to represent a death six years earlier. For 1963 to 1971 transfers, we used a three-year adjustment; for 1972 to 1985, two years; and for 1986 to 1995, one year.

Imputation of Date of Birth

For 1,448 otherwise complete Navy records, date of birth was missing. Since the proportional hazards and standardized mortality analyses we used require age information, we devised a date-of-birth imputation procedure. For individuals with known dates of birth in the participant and control cohorts, date of birth was associated with paygrade and military rating. We therefore used a missing data imputation technique (hot deck technique, Naus 1975) to assign a date of birth from a randomly selected member of the cohort. Records were first matched according to exact rating (e.g., Seaman) and paygrade (e.g., E2); those having no matching rated individual were assigned based on paygrade.

Summary

Table 10-5 describes the extent and distribution of missing data items by the important analysis categories of exposure and outcome.

TABLE 10-5. Number and Percent of Records With Missing Needed Data Item

 

 

Participant Cohort

Control Cohort

Characteristic

Denominator

No.

%

No.

%

Date of birth without imputation

All

873

2.25

610

1.74

Date of birth with imputations

All

27

0.07

8

0.02

Occupation

Enlisted

2

0.01

8

0.03

Paygrade

All

2

0.01

8

0.02

Date of death without imputation

Dead

401

3.32

166

1.54

Date of death with imputations

Dead

17

0.14

20

0.19

Cause of death

Dead

1,650

13.64

1,146

10.61

Completeness of Vital Status Ascertainment

Because recorded vital status is the main outcome in this study, differences in success in its ascertainment could distort the association we observe between exposure and that outcome. We discuss this in great detail in the preceding

Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×

chapter (Chapter 9). In Tables 10-6 and 10-7 we present data on the follow-up of mortality status of participants and controls. Subjects are divided into those (1) known to have died and who have coded cause of death, (2) known to have died but with no cause of death available, (3) presumed alive (i.e., found on the Beneficiary Identification and Records Locator Subsystem [BIRLS] without a date of death or a FARC location), and (4) those not found on BIRLS, whom we consider lost to follow-up.

TABLE 10-6. Vital Status on Follow-Up

 

Participants

Controls

Vital Status on Follow-Up

No.

%

No.

%

Dead

12,093

31.3

10,806

30.8

Presumed alive

21,770

56.3

20,319

58.0

Lost to follow-up

4,805

12.4

3,911

11.2

Total

38,668

100

35,036

100

TABLE 10-7. Information Available on Deaths

 

Participants

Controls

Data Available on Deaths

No.

%

No.

%

Date and Cause

10,436

86.3

9,649

89.3

Date only

1,639

13.6

1,135

10.5

Cause only

7

0.1

10

0.1

Neither Cause nor Date

10

0.1

10

0.1

Blank

1

0.0

2

0.0

Total Dead

12,093

100

10,806

100

Mortality Comparisons

The overall goal of the analysis to is compare mortality among CROSSROADS participants with that among controls. Under the null hypothesis, which is usually defined as the absence of an association, there would be no differences in mortality rates between the participants and the controls. In particular, if participation at CROSSROADS had no effect, we would find no significant difference in overall mortality.

A secondary hypothesis arises from concerns that radiation exposure at CROSSROADS could be the cause of any effect that may be seen among participants relative to nonparticipating controls. Under this null hypothesis there would be no significant trend observed across boarding party participants (more exposure surrogate), non-boarding-party participants (less exposure surrogate), and nonparticipant controls (no exposure surrogate) in all-malignancy or leukemia mortality. Similarly, mortality experience in the

Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×

Engineering & Hull exposure group would be no different than that in the other enlisted group.

Multivariate Analyses

Cox Proportional Hazards Model

Using survival time since Operation CROSSROADS as the dependent variable, we use the proportional hazards model to estimate the risks associated with possible explanatory factors (e.g., participant status, boarder status, occupational specialty), including exposure, while mathematically adjusting for potential confounders (e.g., age, rank, rate, paygrade). This model, first formulated by Cox (1972), can take into account the varied lengths of follow-up and other time-dependent effects. We implemented the Cox analysis using the PHREG procedure in SAS (SAS Institute 1992). It is a semiparametric model that ''measures the relative risk of death or disease in (infinitesimally) small time intervals under the assumption that the relative risk is constant over the follow-up period (Ingram and Makuc 1994).''

We used the Cox model with survival time as the response variable; vital status as the censoring variable;22 and age, participant status, paygrade, Engineering & Hull status, and boarder status as explanatory variables. These covariate content areas were chosen before data collection; decisions regarding category divisions were informed by data availability and distributions. Variable definitions are found in Table 8.

Although the distributions of characteristics such as age and paygrade are similar for the participant and control cohorts, they are not identical, and thus we have adjusted for them in the analyses. This model estimates relative risk for one characteristic after removing the variation due to the distribution of other variables in the model. We present the output as relative rate ratios with 95 percent confidence intervals. All statistical tests are two-sided.

We examined the data for all-cause mortality, all-cancer mortality, leukemia mortality, and mortality from specific causes preselected because of concern or knowledge about radiogenicity. We tested a range of possible time-related interactions with exposure. To provide perspective, we also selected several broad categories of cause. The cause-of-death analysis categories are listed in Table 10-9 in decreasing categories of aggregation.

22  

 For all-cause mortality, survival time is measured from I July 1946 to date of death; survivors are right censored at the end of the study (31 December 1992). For cause-specific mortality, survival time is measured from 1 July 1946 to date of death due to the specific cause; other deaths are right censored at time of death; survivors are right censored at the end of the study.

Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×

Table 10-8. Definitions of Analysis Variables

Variable Name

Definition*

Vital status

1 = Dead; 0 = Not Known Dead

Age at shot

Continuous variable calculated by date of shot minus date of birth

Survival time

Continuous variable calculated by date of death minus date of shot

Participant status

1 = Participant; 0 = Control

Boarder status

3-Level set of indicator variables representing boarding participants, nonboarding participants, and nonparticipant controls.

Paygrade

Paygrades summarized in four levels (junior enlisted, El–E3; mid-level enlisted, E4–E5; senior enlisted, E6–E7; and Officers (commissioned and warrant, O1–O10 and W1–W4).

Occupation 1

3-Level set of indicator variables representing: Engineering & Hull, all other enlisted occupational specialties, and all officers.

Occupation 2

7-Level set of indicator variables combining information from 3-level Occupation I with 4-level paygrade categories.

*See Chapter 8 for a fuller description.

Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×

TABLE 10-9. ICD9 Mortality Codes Used as Case Definitions for Analyses

Case definitiona

ICD9 mortality codes

All causes

0010–9999

All malignancies

1400–2021, 2024, 2027–2089, 2384, 2386, 2898

Buccal cancer

1400–1499

Digestive cancer

1500–1590, 1592–1599

   Esophagal cancer

1500–1509

   Stomach cancer

1510–1519

   Large intestine cancer

1530–1539, 1590

   Rectal cancer

1540–1542, 1544–1549

   Liver cancer

1550–1551, 1553–1569

   Pancreatic cancer

1570–1579

Respiratory cancer

1600–1639, 1642, 1643, 1648, 1649, 1650–1659

   Lung cancer

1620–1629

Bone cancer

1700–1709

Skin cancer

1720–1739

Prostate cancer

1850–1859

Testicular cancer

1860–1876, 1878–1879

Bladder cancer

1880–1886, 1888–1889

Kidney cancer

1890–1899, 1887

Eye cancer

1900–1909

Brain and other CNS cancer

1910–1929

Thyroid cancer

1930–1939

All lymphopoietic cancer

2000–2021, 2024, 2027–2089, 2384, 2386, 2898

   Lymphosarcoma and reticulosarcoma

2000–2009

   Hodgkin's disease

2010–2019

   Leukemiab and aleukemia

2040–2089, 2024, 2031

   Other lymphatic tissue cancer

2020–2021, 2027–2030, 2032–2039, 2384, 2386, 2071, 2053, 1591

   Multiple myeloma

2030, 2386

Benign neoplasms

2100–2376, 2378–2383, 2388–2399

Circulatory system disease

3900–4599

Respiratory disease

4600–5199

Digestive system disease

5200–5799

All external causes of death

8000–9989

   All accidents

8000–9499

      Motor vehicle accidents

8100–8299

   Suicide

9500–9599

Infectious and parasitic diseases

001–139

Endocrine, nutritional, and metabolic diseases and immunity disorders

240–279

Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×

Case definitiona

ICD9 mortality codes

Diseases of the blood and blood-forming organs

280–289

Mental disorders

290–319

Diseases of the nervous system and sense organs

320–389

Diseases of the genitourinary system

580–629

Diseases of the skin and subcutaneous tissue

680–709

Diseases of the musculoskeletal system and connective tissue

710–739

Congenital anomalies

740–759

Symptoms, signs, and ill-defined conditions

780–799

a Case definitions chosen mostly from NCI updated mortality rates (NCI 1995); additional broad categories use ICD9 chapter headings as organizers (WHO 1995).

b For the proportional hazards analysis of leukemia, we excluded chronic lymphoid leukemia because it has not been identified as radiogenic. The software package for SMR calculations, however, includes CLL (Preston et al. 1993).

Standardized Mortality Ratios

For comparison with other atomic veteran studies (Darby 1988, 1993; NRC 1985) we calculated standardized mortality ratios (SMRs) for all-cause mortality, all malignancies, and leukemias for the Navy, Marine, and Army cohorts. To control for age and social factors in all-cause and all-malignancy categories, we calculated separate SMRs by the seven-level "Occupation 2" variable described in Table 8-2, Chapter 8. For leukemias, where there were few cases, we collapsed the seven levels over rank and rating. We expected that both participants and controls would exhibit a "healthy soldier effect." The details of this secondary analysis are presented in Appendix C.

An off-raised and truly considerable drawback to SMR use in studies of occupational-type exposures is the healthy worker—or soldier (sailor)—effect described in Chapter 3. In fact, an earlier National Research Council mortality study of atmospheric nuclear tests and mortality (Robinette et al. 1985) was criticized for using SMRs as its sole risk comparison. The study we report here was designed to include a military reference cohort to provide a finer comparison. The SMR comparison to the U.S. white male population23 of the period under study adds, as mentioned above, a perspective that is useful as long as one keeps its limitations in mind.

23  

 Navy personnel in 1946 were predominantly white; we have no individual data on race.

Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×

Analysis of Army (Including Army Air Corps) and Marine Data

The Navy constituted 91 percent of the CROSSROADS cohort, has occupational specialty information available on its enlisted component, has the largest availability of identification data (availability of date of birth in participants, 97.8 percent, and controls, 98.3 percent) and the most complete cause-of-death information (89.3 percent controls/86.3 percent participants). For that reason we chose to do our primary analysis on the Navy data.

For the Army, which was 7.8 percent of the CROSSROADS cohort, fully 20.4 percent of the dates of birth in the participants were missing and had to be imputed (as compared to 1.8 percent for controls). In addition, the availability of causes of death was lower for Army than for Navy personnel (87.9 percent for participants, 85.9 percent for controls). The quality for the Marines was comparable to that of the Navy, but the Marines constitute a comparatively small number of individuals (557 participants), making detailed analysis of the group impossible from a statistical point of view. Because the Marines do not have any specialty information available for their enlisted ranks, we were reluctant to mix them in with the Navy data.

As a result of these factors, we chose to:

  • analyze the Army and the Marine data for differences in all-cause, all-cancer, and leukemia mortality using the proportional hazards model developed for the Navy without the occupational specialty variables, and
  • compute SMRs on the Army and Marines only for all-cause, all-cancer, and leukemia mortality.

We do these analyses with some hesitation, given the limitations in the Army data and the small number of Marines, and we present the results solely for completeness. The conclusions of the study are based entirely upon our findings among the Navy personnel.

Not the Subject of Analysis in This Report

As we have stated before, this study was designed and funded subject to several unavoidable constraints, among which are: dosimetry is incomplete; military records do not keep the type of data often required for epidemiologic investigation, and those data items that are kept are not always complete; the U.S. does not have a centralized national vital statistics database for individuals that spans the time period 1946 until now; cause-of-death data have known limitations; Operation CROSSROADS was only one event in a lifetime of physical and psychological events for the participants; and few women were assigned to units included in participant and control cohorts.

Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×

For these reasons, this report neither explores nor addresses all the interesting facets of possible exposure-outcome associations. It can, therefore, neither reassure nor vindicate those who feel strongly about the nature of many of those associations. Areas of inquiry into which we have not delved in this study but for which we could imagine a study design include:

  • exposure-outcome analyses based on exact dosimetry estimates calculated for a subset of the overall study population;
  • fuller examination of cause of death, looking beyond the underlying cause to all associated or contributory causes listed on the death certificate; and
  • detailed analysis of the participants who served in the Marines and Army (including the Army Air Corps) in CROSSROADS and their controls.

Unfortunately, the following group of topics may never be well studied in this observational cohort due to reasons including very small numbers; the nonexistence of necessary exposure information; and the unfeasibility, if not impossibility, of tracking health outcomes other than death:

  • unique aspects, if any, of the exposure-outcome relationship in women;
  • possible effects of participation or other measures of exposure on outcomes other than mortality, looking at morbidity rates for the diseases considered in the mortality study (e.g., skin cancer) and for other diseases and conditions believed to be radiogenic (e.g., cataracts);
  • adverse reproductive outcomes;24
  • more finely defined categories of military occupation, for officers and non-Navy enlisted personnel for whom no occupation data is available; and
  • the interrelationships of other, non-CROSSROADS, risk factors accruing before, during, and after the Operation CROSSROADS activities, including an overlapping array of exposures that could be chemical and physical (occupational, environmental, behavioral); socioeconomic (education, income, occupation); geographic; and medical (comorbidities). Not the least of these is the possibility that many of the participants, as a result of their special radiological training for Operation CROSSROADS, may have gone on to careers associated with radiation.

24  

 Feasibility is discussed in Institute of Medicine, Medical Follow-up Agency. Adverse Reproductive Outcomes in Families of Atomic Veterans: The Feasibility of Epidemiologic Studies. Washington, D.C.: National Academy Press, 1995.

Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×
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Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×
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Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×
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Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×
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Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×
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Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×
Page54
Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×
Page55
Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×
Page56
Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
×
Page57
Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
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Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
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Page59
Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
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Suggested Citation:"Characterization of the Cohorts and Analysis Plan." Institute of Medicine. 1996. Mortality of Veteran Participants in the CROSSROADS Nuclear Test. Washington, DC: The National Academies Press. doi: 10.17226/5428.
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In 1946, approximately 40,000 U.S. military personnel participated in Operation CROSSROADS, an atmospheric nuclear test that took place at Bikini Atoll in the Marshall Islands. Congress passed a law directing the Veterans Administration to determine whether there were any long-term adverse health effects associated with exposure to ionizing radiation from the detonation of nuclear devices. This book contains the results of an extensive epidemiological study of the mortality of participants compared with a similar group of nonparticipants. Topics of discussion include a breakdown of the study rationale; an overview of other studies of veteran participants in nuclear tests; and descriptions of Operation CROSSROADS, data sources for the study, participant and comparison cohorts, exposure details, mortality ascertainment, and findings and conclusions.

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