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Table 5 Subgroup analyses for the association between whole grain intake and breast cancer risk

From: Association between whole grain intake and breast cancer risk: a systematic review and meta-analysis of observational studies

Subgroups No. of studies RR (95% CI) P Heterogeneity χ2 I2(%) P for heterogeneity
Overall 11 0.84 (0.74,0.96) 0.009 27.6 63.8 0.002
Study design
 Cohort study 4 0.96 (0.82,1.14) 0.69 9.0 66.7 0.029
 Case-control study 7 0.69 (0.56, 0.87) 0.001 14.3 58.2 0.026
Sample size
  ≤ 2300, below median 5 0.55 (0.43, 0.70) < 0.001 1.1 0.0 0.893
  > 2300, above median 6 0.94 (0.85,1.04) 0.25 9.9 49.8 0.077
Publication year
 After 2008 6 0.87 (0.74,1.03) 0.12 13.4 62.9 0.019
 Before 2008 5 0.75 (0.58,0.97) 0.032 14.1 71.6 0.007
Number of adjustment for covariates
  ≤ 7 5 0.80 (0.64,0.99) 0.04 11.1 64.2 0.025
  > 7 6 0.84 (0.69,1.04) 0.11 16.3 69.4 0.006
Study quality score
  ≤ 7 6 0.77 (0.63, 0.96) 0.019 13.0 61.6 0.023
  > 7 5 0.87 (0.71,1.07) 0.19 14.3 72.0 0.006