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Table 3 Test-retest reproducibility of food groups for the food-frequency questionnaire (n = 21)

From: Reproducibility and relative validity of a newly developed web-based food-frequency questionnaire for assessment of preconception diet

  FFQ 1 FFQ 2 Spearman’s r P CC % GM % Kappa k P
Median (P25, P75) Median (P25, P75)
Milk, yoghurt, milk dessert (ml/day) 184 (103, 335) 168 (54, 266) 0.81 < 0.001 62 0 0.43 0.006
Cheese (g/day) 20 (10, 31) 18 (2.9, 35) 0.82 < 0.001 67 0 0.50 0.001
Eggs (g/day) 18 (16, 54) 18 (12, 66) 0.90 < 0.001 67 0 0.51 < 0.001
Poultry (g/day) 22 (11, 54) 21 (11, 31) 0.76 < 0.001 71 5 0.57 < 0.001
Red meat, non-processed (g/day) 12 (10, 20) 20 (8.5, 28) 0.85 < 0.001 62 0 0.43 0.005
Red meat, processed (g/day) 14 (1.8, 19) 9.3 (1.8, 21) 0.22 0.331 33 14 0.01 0.946
Liver-pate (g/day) 0 (0, 7.1) 2.9 (0, 7.1) 0.69 0.001 71 10 0.54 0.001
Meat dishes (g/day) 45 (23, 66) 45 (21, 67) 0.66 0.001 52 5 0.29 0.063
Fatty fish (g/day) 11 (5.4, 21) 11 (11, 21) 0.40 0.073 71 10 0.56 < 0.001
Lean fish (g/day) 14 (0, 29) 14 (0, 14) 0.79 < 0.001 71 0 0.56 < 0.001
Fish spread (g/day) 7.9 (0, 14) 5.7 (0, 22) 0.70 < 0.001 71 5 0.57 < 0.001
Fish dishes (g/day) 11 (0, 11) 11 (0, 11) 0.46 0.035 43 14 0.23 0.033
Breakfast cereal, high grain (g/day) 14 (7.1, 107) 36 (7.1, 100) 0.83 < 0.001 71 0 0.57 < 0.001
Rice, pasta, noodle (g/day) 76 (46, 113) 76 (43, 133) 0.55 0.010 52 10 0.28 0.066
Bread, crispbread, low fibre (g/day) 5.7 (0, 17) 5.7 (0, 23) 0.75 < 0.001 86 5 0.78 < 0.001
Bread, crispbread, high fibre (g/day) 102 (34, 142) 102 (38, 123) 0.76 < 0.001 71 5 0.57 < 0.001
Nuts, almonds (g/day) 1.4 (0.7, 7.1) 2.9 (0.7, 7.1) 0.64 0.002 71 5 0.56 < 0.001
Potatoes (g/day) 33 (20, 68) 31 (15, 72) 0.76 < 0.001 62 5 0.43 0.006
Vegetables (g/day) 116 (75, 189) 102 (69, 163) 0.84 < 0.001 71 5 0.57 < 0.001
Fruits (g/day) 172 (50, 249) 133 (58, 304) 0.76 < 0.001 67 0 0.50 0.001
Sugar, sweets, desserts(g/day) 28 (12, 37) 25 (12, 39) 0.70 < 0.001 57 5 0.36 0.020
Oils, butter, margarine (g/day) 2.1 (0.4, 16) 2.9 (0, 10) 0.93 < 0.001 81 0 0.71 < 0.001
Coffee, tea, water (ml/day) 964 (789, 1323) 964 (735, 1196) 0.90 < 0.001 76 0 0.64 < 0.001
Juice, sweet drinks (ml/day) 171 (111, 257) 200 (86, 489) 0.72 < 0.001 52 0 0.29 0.060
Alcohol (ml/day) 53 (1.4, 154) 69 (19, 111) 0.83 < 0.001 81 5 0.72 < 0.001
Pizza (g/day) 43 (21, 43) 21 (21, 43) 0.38 0.088 33 5 0.16 0.038
Salty snacks (g/day) 5.7 (2.9, 8.6) 5.7 (2.9, 8.6) 0.58 0.006 48 10 0.21 0.156
Mixed dishes (g/day) 84 (79, 173) 84 (70, 154) 0.75 < 0.001 67 5 0.49 0.001
  1. Food intake (gram/milliliter per day) for food groups (median, 25th and 75th percentile, Spearman’s rank correlation coefficient, percent correctly classified (CC) and grossly misclassified (GM) into tertiles of intake, Cohen’s Kappa value). Statistically significant p-values marked in bold