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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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