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Table 4 Measures of reproducibility for the daily intake of energy and selected nutrients 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
Nutrient Mean SDa Mean SD Mean 95% CIb Mean ± 2 SDc r 95% CI r s
Energy (kJ) 6571 1748 6400 1732 170.2 (91.5, 249.0) (-2801, 3142) 0.64 (0.60, 0.67) 0.63
Protein (g) 73.6 21.3 71.5 21.0 2.1 (1.0, 3.1) (-36, 40) 0.60 (0.56, 0.63) 0.60
Total fat (g) 60.0 20.1 58.4 19.4 1.6 (0.7, 2.5) (-32, 35) 0.63 (0.60, 0.66) 0.64
   Polyunsaturated fat (g) 11.0 4.4 10.7 4.3 0.2 (0.1, 0.4) (-7, 8) 0.65 (0.62, 0.68) 0.66
Total carbohydrate (g) 179.4 49.9 174.0 50.9 5.4 (3.2, 7.6) (-77, 87) 0.67 (0.64, 0.70) 0.67
   Dietary fiber (g) 19.6 6.2 18.6 5.9 1.0 (0.7, 1.2) (-9, 11) 0.67 (0.64, 0.70) 0.66
   Sugar (g) 22.1 13.4 22.3 13.7 -0.2 (-0.8, 0.4) (-21, 21) 0.70 (0.67, 0.72) 0.71
Alcohol (g) 2.2 3.2 2.8 3.5 -0.6 (-0.7, -0.5) (-6, 4) 0.72 (0.69, 0.75) 0.77
Retinol (REd, μg) 1192 490 1142 482 50.3 (29.3, 71.3) (-742, 843) 0.67 (0.64, 0.70) 0.66
Vitamin D (μg) 12.4 9.0 12.3 8.5 0.1 (-0.3, 0.5) (-14, 14) 0.69 (0.66, 0.72) 0.70
Vitamin E (mg) 11.0 7.4 11.0 7.4 0.0 (-0.3, 0.3) (-10, 10) 0.78 (0.76, 0.80) 0.73
Vitamin C (mg) 106 50 96 48 9.6 (7.5, 11.7) (-69, 88) 0.68 (0.65, 0.70) 0.69
Calcium (mg) 624 246 600 248 23.2 (10.8, 35.6) (-445, 492) 0.55 (0.51, 0.59) 0.60
% energy from protein 19.2 2.9 19.1 3.0 0.0 (-0.1, 0.2) (-5, 5) 0.70 (0.67, 0.72) 0.69
% energy from fat 33.5 4.8 33.5 4.8 0.0 (-0.3, 0.2) (-8, 8) 0.65 (0.62, 0.68) 0.65
% energy from carbohydrate 46.5 5.8 46.3 5.9 0.3 (0.0, 0.6) (-10, 10) 0.64 (0.61, 0.67) 0.63
% energy from sugar 5.7 3.0 5.8 3.0 -0.2 (-0.3, -0.1) (-5, 5) 0.68 (0.65, 0.71) 0.68
% energy from alcohol 1.0 1.6 1.4 1.8 -0.3 (-0.4, -0.2) (-3, 2) 0.74 (0.72, 0.76) 0.78
  1. aSD = Standard deviation, bCI = Confidence interval, cReferred to as limits of agreement in the text, dRetinol equivalents