Reproducibility and relative validity of a food frequency questionnaire for a diet-related study in a rural Chinese population

Table 3 Spearman correlation coefficients, percentage of agreement and weighted kappa statistic between FFQ1 and FFQ2

	Spearman correlation coefficients		Percentage of agreement (%)			κ^{a c}
	Crude ^b	Energy adjusted ^b	Same tertile	Adjacent tertile	Extreme tertile	κ^{a c}
Energy	0.73		69.48	27.27	3.25	0.62
Protein	0.75	0.73	64.94	32.47	2.60	0.58
Fat	0.75	0.70	66.23	31.17	2.60	0.59
Fiber	0.74	0.73	59.09	37.01	3.90	0.50
Carbohydrate	0.74	0.71	71.43	24.68	3.90	0.63
Carotene	0.72	0.71	59.74	32.47	7.79	0.46
Retinol	0.77	0.74	64.94	32.47	2.60	0.58
Thiamine	0.79	0.71	67.53	30.52	1.95	0.61
Riboflavin	0.79	0.79	68.18	30.52	1.30	0.63
Niacin	0.66	0.63	64.94	31.17	3.90	0.56
Vitamin C	0.70	0.70	58.44	35.06	6.49	0.46
Vitamin E	0.71	0.74	68.83	27.92	3.25	0.61
Calcium	0.68	0.71	57.79	38.96	3.25	0.49
Iron	0.61	0.71	64.94	27.28	7.79	0.52
Zinc	0.79	0.65	66.88	29.87	3.25	0.59
Selenium	0.81	0.76	69.48	27.27	3.25	0.62
Eggs	0.87	0.86	79.87	18.18	1.95	0.75
Red meat	0.82	0.71	80.52	16.23	3.25	0.74
White meat	0.79	0.65	67.78	29.22	3.00	0.53
Soy products	0.80	0.80	79.37	15.87	4.76	0.45
Fresh vegetables	0.69	0.68	63.64	31.82	4.55	0.56
Processed vegetables	0.82	0.83	86.36	12.99	0.65	0.72
Fruits	0.92	0.92	83.77	15.58	0.65	0.81
Nuts and seeds	0.58	0.62	59.74	38.31	1.95	0.47
Cereals	0.74	0.68	68.83	27.27	3.90	0.60
Tuber crop	0.70	0.64	55.45	38.86	5.69	0.46

^aAbbreviation: FFQ1, the first survey of food frequency questionnaire; FFQ2, the second survey of food frequency questionnaire; κ statistics, for weighted kappa test;
^bFor Crude and energy-adjusted Spearman correlation coefficients, all values were significant (P < 0.05)
^cAll weighted kappa coefficients were significant (P < 0.05) except for vitamin E and white meat

ISSN: 1475-2891