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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
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Nutrition Journal

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