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Table 3 Measures of reproducibility for the intake of food groups (g/day) in the test and retest food frequency questionnaire (FFQ), n = 1370

From: Test-retest reproducibility of a food frequency questionnaire (FFQ) and estimated effects on disease risk in the Norwegian Women and Cancer Study (NOWAC)

  Test (FFQ1) Retest (FFQ2) Within person differences (FFQ1-FFQ2) Pearson Spearman
Food group (no. items) Mean SDa Mean SD Mean 95% CIb Mean ± 2 SDc r 95% CI r s
Potatoes (1) 107 56 103 57 3.4 (1.2, 5.7) (-80, 87) 0.72 (0.69, 0.75) 0.70
Vegetables (7) 118 75 116 71 1.3 (-1.7, 4.4) (-112, 115) 0.69 (0.66, 0.72) 0.71
Fruits (5) 200 127 185 130 15.4 (10.0, 20.8) (-185, 216) 0.68 (0.65, 0.71) 0.71
Dairy products (12) 207 161 203 159 3.3 (-4.0, 10.6) (-266, 273) 0.63 (0.60, 0.66) 0.76
   Drinking milk, yogurt, cheese on bread (9) 181 158 179 154 2.4 (-4.8, 9.7) (-264, 269) 0.62 (0.58, 0.65) 0.74
   Cream desserts, milk based puddings (3) 25 25 25 26 0.8 (-0.2, 1.8) (-36, 38) 0.72 (0.70, 0.75) 0.80
Cereal and cereal products (7) 161 65 154 63 7.0 (3.8, 10.2) (-112, 126) 0.55 (0.52, 0.59) 0.55
   Bread, crisp bread, breakfast cereal (5) 131 61 124 57 6.3 (3.3, 9.3) (-103, 116) 0.55 (0.52, 0.59) 0.55
   Pasta and rice (2) 30 23 30 22 0.7 (-0.2, 1.7) (-36, 37) 0.66 (0.63, 0.69) 0.68
Meat and meat products (11) 96 46 95 45 0.2 (-2.0, 2.4) (-81, 81) 0.59 (0.55, 0.62) 0.58
   Read meat and chicken (5) 28 17 29 17 -1.1 (-1.9, -0.3) (-31, 29) 0.62 (0.58, 0.65) 0.63
   Processed meat (6) 68 37 67 37 1.3 (-0.6, 3.1) (-66, 69) 0.57 (0.53, 0.60) 0.56
Fish and shellfish (17) 128 77 123 73 5.1 (1.9, 8.4) (-116, 127) 0.66 (0.63, 0.69) 0.69
   Whole fish (filets, steaks) and shellfish (8) 81 60 77 59 4.2 (1.4, 7.1) (-100, 108) 0.60 (0.57, 0.63) 0.66
   Fish products (9) 47 30 46 28 0.9 (-0.5, 2.3) (-51, 53) 0.58 (0.54, 0.61) 0.59
Eggs (1) 14 11 14 11 -0.7 (-1.1, -0.2) (-16, 15) 0.72 (0.69, 0.74) 0.70
Fat (margarine, butter) on bread (7) 12 13 11 11 0.8 (0.3, 1.2) (-17, 18) 0.72 (0.70, 0.75) 0.78
Cakes (6) 35 26 36 27 -0.3 (-1.5, 0.9) (-44, 43) 0.65 (0.62, 0.68) 0.65
Orange juice, soft drinks, diluted syrups (3) 106 121 112 130 -6.6 (-12.1, -1.0) (-211, 198) 0.66 (0.62, 0.68) 0.70
Coffee (boiled, filtered, instant) (3) 368 249 366 258 1.5 (-9.3, 12.4) (-400, 403) 0.67 (0.64, 0.70) 0.73
Alcoholic beverages (wine, beer, spirits) (3) 32 51 41 60 -9.1 (-11.5, -6.7) (-98, 80) 0.68 (0.65, 0.71) 0.76
Condiments and sauces for fish (5) 9 9 9 9 0.3 (-0.2, 0.8) (-18, 18) 0.50 (0.46, 0.54) 0.58
Sweets and salty snacks (6) 25 19 25 19 0.1 (-0.8, 0.9) (-31, 31) 0.66 (0.63, 0.69) 0.71
Cod liver oil supplements (4) 2 3 2 3 -0.1 (-0.2, 0.0) (-4, 4) 0.79 (0.77, 0.81) 0.74
  1. aSD = Standard deviation, bCI = Confidence interval, cReferred to as "limits of agreement" in the text