Table 2 Reliability coefficients (95% confidence intervals: 95% CI) for food items that were measured in both periods (late childhood, 6–12 years and adolescence, 13–18 years).

From: Test-retest reliability of a computer-assisted self-administered questionnaire on early life exposure in a nasopharyngeal carcinoma case-control study

Food frequency questionnaire		Coefficients (N, methods^‡), 95% CIs
Food frequency questionnaire		Age 6–12 years	Age 13–18 years
Animal liver	Frequency	0.69 (138), 0.57–0.78	0.57 (139), 0.44–0.67
Animal liver	Portion	0.20 (99), -0.19, 0.46^#	0.46 (102), 0.29–0.60
Fresh milk	Frequency	0.70 (139), 0.57–0.79	0.74 (139), 0.65–0.80
Fresh milk	Portion	0.65 (70), 0.44–0.79	0.53 (79), 0.35–0.67
Powdered milk	Frequency	0.51 (138), 0.31–0.65	0.44 (139), 0.30–0.57
Powdered milk	Portion	0.40 (30), -0.28, 0.72^#	0.35 (30), 0.01–0.63^†
Soybean milk	Frequency	0.73 (139), 0.63–0.81	0.63 (137), 0.51–0.72
Soybean milk	Portion	0.51 (82), 0.24–0.69	0.44 (96), 0.27–0.59
Bean curd	Frequency	0.73 (139), 0.63–0.81	0.68 (139), 0.58–0.76
Bean curd	Portion	0.51 (82), 0.24–0.69	0.36 (112), 0.19–0.51
Type of salted fish		0.28 (140, K), 0.18–0.38	0.31 (139, K), 0.21–0.41
Mouldy salted fish	Frequency	0.77 (33), 0.53–0.89	0.85 (26), 0.68–0.93
Mouldy salted fish	Portion	0.85 (33), 0.70–0.93	0.69 (26), 0.43–0.85
Firmed salted fish	Frequency	0.84 (29), 0.65–0.92	0.64 (36), 0.40–0.80
Firmed salted fish	Portion	0.71 (29), 0.37–0.86	0.56 (34), 0.28–0.76
Other types of salted fish	Frequency	0.94 (9), 0.75–0.99	0.94 (13), 0.81–0.98
Other types of salted fish	Portion	0.92 (8), 0.64–0.98	0.38 (13), -0.22, 0.76^#
Preserved egg	Frequency	0.62 (139), 0.47–0.73	0.62 (139), 0.51–0.72
Preserved egg	Portion	0.64 (111), 0.47–0.75	0.48 (112), 0.33–0.61
Preserved vegetable	Frequency	0.67 (138), 0.54–0.77	0.59 (139), 0.47–0.69
Preserved vegetable	Portion	0.54 (98), 0.31–0.69	0.47 (114), 0.31–0.60
Preserved fruit	Frequency	0.61 (138), 0.50–0.71	0.66 (140), 0.55–0.74
Preserved fruit	Portion	0.61 (81), 0.39–0.75	0.38 (90), 0.19–0.55

Frequency: Never/Less than once a month/Once a month/1–3 per week/4–6 per week/1–2 per day/3+ per day). Portion: Small/Medium/Large. K: Cohen’s kappa. ^‡Intra-class correlation coefficient was used in most items, unless otherwise stated. Coefficients: 0 to <0.2, poor; 0.2 to <0.4, fair; 0.4 to <0.6, moderate; 0.6 to <0.8, substantial; and 0.8 to 1.0, almost perfect. No differences by different life periods (difference among coefficients >0.30, and tested by a Fisher Z transformation [p < 0.01]) were found. All the coefficients above were p < 0.01, unless otherwise stated (^†0.01 ≤ p ≤ 0.05; ^#p > 0.05 [-x, x]).

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Table 2 Reliability coefficients (95% confidence intervals: 95% CI) for food items that were measured in both periods (late childhood, 6–12 years and adolescence, 13–18 years).

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