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Table 1 Characteristics of Millennium Cohort Study participants according to response to follow-up and multivariable regression coefficients predicting response (N = 76,775)

From: Assessing nonresponse bias at follow-up in a large prospective cohort of relatively young and mobile military service members

Characteristic Follow-up response status Multivariable logistic regression model
  Follow-up responder
N= 54,960 		Follow-up nonresponder
N= 21,815 		Beta (standard error) Pvalue
  n % n %   
Intercept      -0.24 (0.07) 0.0006
Demographic and military characteristics obtained from the Defense Manpower Data Center       
Gender       
   Male 40,311 71.7 15,895 28.3 Ref <0.0001
   Female 14,649 71.2 5,920 28.8 0.36 (0.07)  
Age group (years)       
   17-24 7,932 54.7 6,576 45.3 Ref <0.0001
   25-34 19,249 71.3 7,766 28.7 0.56 (0.08)  
   35-44 19,600 77.4 5,727 22.6 1.03 (0.09)  
   >44 8,179 82.4 1,746 17.6 1.26 (0.12)  
Race/ethnicity       
   White, non-Hispanic 38,965 72.9 14,468 27.1 Ref <0.0001
   Black, non-Hispanic 6,721 63.5 3,859 36.5 -0.49 (0.03)  
   Asian/Pacific Islander 4,859 80.1 1,207 19.9 -0.02 (0.05)  
   Native American 453 66.8 225 33.2 -0.10 (0.14)  
   Hispanic 3,202 64.9 1,728 35.1 -0.30 (0.05)  
   Other 760 69.9 328 30.1 -0.19 (0.09)  
Education       
   Less than high school 2,957 62.9 1,743 37.1 Ref <0.0001
   High school diploma or equivalent 21,053 64.1 11,802 35.9 0.28 (0.07)  
   Some college 14,593 74.4 5,011 25.6 0.66 (0.08)  
   Bachelor's degree 10,353 81.7 2,312 18.3 0.76 (0.16)  
   Postgraduate 6,004 86.4 947 13.6 2.37 (1.07)  
Marital status       
   Never married 14,548 63.0 8,541 37.0 Ref <0.0001
   Married 36,484 75.3 11,949 24.7 0.10 (0.02)  
   Divorced/widowed/separated 3,928 74.8 1,325 25.2 0.04 (0.04)  
Branch of service       
   Army 26,261 72.2 10,118 27.8 Ref <0.0001
   Navy/Coast Guard 9,918 70.0 4,259 30.0 -0.20 (0.03)  
   Marines 2,257 57.6 1,659 42.4 -0.43 (0.05)  
   Air Force 16,524 74.1 5,782 25.9 -0.24 (0.03)  
Service component       
   Reserve/Guard 24,084 73.0 8,928 27.0 Ref <0.0001
   Active duty 30,876 70.6 12,887 29.4 0.44 (0.02)  
Military pay grade       
   Enlisted 40,089 67.8 19,046 32.2 Ref 0.0005
   Warrant officer 1,168 84.5 214 15.5 0.23 (0.10)  
   Commissioned officer 13,703 84.3 2,555 15.7 0.20 (0.07)  
Occupational category       
   Combat specialists 11,212 73.0 4,153 27.0 Ref <0.0001
   Electronic equipment repair 5,050 74.6 1,717 25.4 0.21 (0.04)  
   Communications/intelligence 3,894 71.9 1,523 28.1 0.16 (0.04)  
   Health care 6,144 77.0 1,837 23.0 0.14 (0.04)  
   Other technical and allied specialists 1,379 70.0 590 30.0 0.08 (0.06)  
   Functional support and administration 11,122 72.4 4,236 27.6 0.11 (0.03)  
   Electrical/mechanical equipment repair 7,627 67.2 3,725 32.8 0.05 (0.03)  
   Craft workers 1,635 68.6 748 31.4 0.08 (0.05)  
   Service and supply 4,680 70.1 1,993 29.9 0.06 (0.04)  
   Students, trainees, and other 2,217 63.2 1,293 36.8 0.02 (0.04)  
Deployment experience between 2001 and 2006a       
   None 40,823 70.8 16,799 29.2 Ref <0.0001
   Deployed 14,137 73.8 5,016 26.2 0.08 (0.02)  
Military status at follow-up       
   Enlisted 34,324 71.7 13,560 28.3 Ref <0.0001
   Officer 14,727 84.5 2,706 15.5 0.76 (0.18)  
   No longer in military, retired 3,848 63.6 2,203 36.4 -1.51 (1.24)  
   No longer in military, other 2,120 38.6 3,373 61.4 -1.03 (0.15)  
Self-reported military, behavioral, and health characteristics       
Self-reported military exposures       
   No reported exposures 39,197 70.9 16,074 29.1 Ref 0.01
   Witnessed a person's death due to war, disaster, or tragic event 12,708 73.2 4,652 26.8 0.05 (0.02)  
   Chemical or biological warfare agents 1,427 72.6 538 27.4 0.12 (0.06)  
   Both 1,628 74.7 551 25.3 0.09 (0.05)  
Chronic drinking       
   No 51,186 72.1 19,811 27.9 Ref 0.0192
   Yes 3,774 65.3 2,004 34.7 -0.07 (0.03)  
Smoking status       
   Nonsmoker 32,102 74.0 11,287 26.0 Ref <0.0001
   Ever/past smoker 13,594 72.8 5,071 27.2 -0.06 (0.02)  
   Current smoker 8,332 64.7 4,538 35.3 -0.22 (0.02)  
   Unknown 932 50.4 919 49.6 -0.97 (0.05)  
Self-reported general health       
   Excellent 11,248 75.0 3,746 25.0 Ref <0.0001
   Very good 22,233 73.3 8,102 26.7 0.06 (0.02)  
   Good 16,222 69.6 7,077 30.4 0.04 (0.03)  
   Fair 3,467 65.4 1,837 34.6 0.02 (0.04)  
   Poor 320 57.9 233 42.1 -0.14 (0.10)  
   Unknown 1,470 64.2 820 35.8 -0.24 (0.05)  
Major depressive disorder       
   No 53,431 72.0 20,818 28.0 Ref 0.0010
   Yes 1,529 60.5 997 39.5 -0.16 (0.05)  
Survey response characteristics       
Early response to baseline questionnaireb       
   No 37,656 68.9 17,019 31.1 Ref <0.0001
   Yes 17,304 78.3 4,796 21.7 0.46 (0.02)  
Interaction terms       
Age group × military status at follow-up interactionc       <0.0001
Education × military status at follow-up interactionc       <0.0001
Gender × educationc       0.0012
Age group × educationc       0.0055
Gender × branch of servicec       0.0239
Race/ethnicity × branch of servicec       0.0021
  1. aDeployment experience from 2001 to 2006 refers to deployments in support of the wars in Iraq and Afghanistan.
  2. bEarly response was defined as completing the questionnaire prior to September 1, 2001, which was within 2 months of enrollment invitation on July 1, 2001.
  3. cEach interaction generated multiple terms. The number of these terms ranged from 4 (gender × education) to 15 (race/ethnicity × branch of service).
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BMC Medical Research Methodology

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