Table 1 Summary of the characteristics of the included studies a
| Â | Overall | Adult | Old | Adolescent |
|---|---|---|---|---|
Range of age (years) | 8–86 | 18–50 | >  50 | 8–17 |
Number of studies | 124 | 78 | 33 | 15 |
Population characteristics | ||||
Total number | 20,830 | 11,336 | 7897 | 1597 |
Sample size | 112 (14–1981) | 102 (20–1623) | 158 (14–1981) | 101 (48–185) |
Distribution of gender | ||||
 Region | ||||
  Africa | 6 (4.88) | 5 (6.49) | 0 (0) | 1 (6.67) |
  Oceania | 8 (6.50) | 5 (6.49) | 2 (6.07) | 1 (6.67) |
  Asia | 37 (30.08) | 22 (28.57) | 11 (33.33) | 4 (26.67) |
  Europe | 35 (28.46) | 22 (28.57) | 10 (30.30) | 4 (26.67) |
  America | 37 (30.08) | 23 (29.87) | 10 (30.30) | 5 (33.33) |
FFQ design characteristics | ||||
 Items of FFQ | ||||
  ≥ 120 | 61 (49.59) | 41 (53.25) | 15 (45.45) | 5 (33.33) |
  < 120 | 62 (50.41) | 36 (46.75) | 18 (54.55) | 10 (66.67) |
 Dietary recall intervals | ||||
  ≥ Previous 12 months | 80 (65.04) | 50 (64.94) | 28 (84.85) | 4 (26.67) |
  < Previous 12 months | 33 (26.83) | 20 (25.97) | 3 (9.09) | 10 (66.67) |
  Not available | 10 (8.13) | 7 (9.09) | 2 (6.06) | 1 (6.667) |
Characteristics of the reproducibility studies | ||||
 Administration mode of FFQ | ||||
  Interview-administered | 44 (35.77) | 29 (37.66) | 12 (36.36) | 4 (26.67) |
  Self-administered | 63 (51.22) | 36 (46.75) | 19 (57.58) | 9 (60.00) |
  Not available | 16 (13.01) | 12 (15.59) | 2 (6.06) | 2 (13.33) |
 Intervals between FFQs | ||||
  < 6 months | 63 (51.22) | 45 (58.44) | 8 (24.24) | 12 (80.00) |
  ≥ 6 months | 55 (44.72) | 29 (37.66) | 23 (69.70) | 3 (20,00) |
  Both intervals | 5 (4.06) | 3 (3.90) | 2 (6.06) | 0 (0) |