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