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Table 3 Subgroup analysis of relative risks for the association between insomnia and depression

From: Insomnia and the risk of depression: a meta-analysis of prospective cohort studies

  No of studies RR (95 % CI) I 2 (%) P value for heterogeneity P value between groups
Mean age at baseline, y
 <60 22 2.50 (1.96, 3.20) 94.70 <0.001 0.31
 ≥60 12 1.87 (1.47, 2.37) 80.70 <0.001
Sex
 Male 3 1.46 (1.13, 1.88) 26.70 0.256 0.48
 Female 3 1.96 (1.05, 3.66) 73.50 <0.001
 Mixed 28 2.41 (1.97, .95) 92.80 <0.001
Study location
 USA 14 3.13 (2.03, 4.85) 89.80 <0.001 0.17
 Europe 14 1.73 (1.43, 2.09) 88.50 <0.001
 Asia 4 2.27 (1.22, 4.21) 90.40 <0.001
 Australia 2 1.79 (0.90, 3.54) 95.90 <0.001
Source of participants*
 General population 25 2.34 (1.85, 2.96) 94.00 <0.001 0.75
 Non-general population 9 2.05 (1.53, 2.74) 78.70 <0.001
Insomnia definition
 Sd, dur and day 11 2.90 (1.78, 4.74) 92.70 <0.001 0.37
 Sd and dur 10 2.21 (1.50, 3.25) 90.30 <0.001
 Sd 13 1.87 (1.53, 2.29) 87.70 <0.001
Type of depression measure
 Self-reported scales 17 2.20 (1.70, 2.86) 94.10 <0.001 0.63
 Physician diagnosis 15 2.27 (1.67, 3.09) 91.80 <0.001
 Combined 2 3.89 (1.73, 8.74) 0.00 0.438
Follow-up duration, y
 <5 22 2.34 (1.84, 2.97) 93.60 <0.001 0.77
 5–10 8 2.37 (1.73, 3.25) 82.30 <0.001
 >10 4 1.88 (1.52, 2.32) 54.60 0.086
Sample size
 <5000 26 2.01 (1.66, 2.44) 86.50 <0.001 0.10
 ≥5000 8 3.12 (2.11, 4.62) 96.40 <0.001
Study quality
 Score >7 8 2.06 (1.60, 2.63) 88.60 <0.001 0.70
 Score ≤ 7 26 2.36 (1.83, 3.03) 93.00 <0.001
Publication year
 Before 2010 19 2.63 (1.95, 3.55) 88.20 <0.001 0.21
 2010–2014 15 1.94 (1.53, 2.45) 94.62 <0.001
Statistical model
 Unadjusted 5 1.78 (1.29, 2.47) 56.00 0.078 0.75
 Adjusted 29 2.31 (1.90, 2.81) 93.40 <0.001
Controlling age in models
 Yes 21 2.64 (2.04, 3.42) 92.30 <0.001 0.09
 No 13 1.75 (1.33, 2.31) 92.50 <0.001
Controlling SES in models
 Yes 17 2.34 (1.81, 3.03) 95.60 <0.001 0.78
 No 17 2.15 (1.74, 2.65) 71.60 <0.001
Controlling smoking status in models
 Yes 7 2.10 (1.45, 3.06) 89.80 <0.001 0.75
 No 27 2.32 (1.88, 2.87) 93.30 <0.001
Controlling alcohol intake in models
 Yes 9 2.47 (1.75, 3.48) 90.90 <0.001 0.69
 No 25 2.19 (1.78, 2.69) 92.00 <0.001
Controlling BMI in models
 Yes 5 2.19 (1.57, 3.06) 85.30 <0.001 0.94
 No 29 2.28 (1.87, 2.78) 92.30 <0.001
  1. Abbreviations: BMI body mass index, dur duration criterion, day daytime consequences criterion, F female, M male, NA not available, SES socioeconomic status, Sd sleep difficulties criterion
  2. *Study population truly or somewhat representative of a community or population-based study defined as general population, and study population was sampled from a special population (such as population from a company, register patients, data from the health insurance company or health examination organization or pregnant), which defined as non-general populations