Hospital Outpatients are Satisfactory for Case-control Studies on Cancer and Diet in China: A Comparison of Population Versus Hospital Controls

Background: To investigate the internal validity of a food-frequency questionnaire (FFQ) developed for usein Chinese women and to compare habitual dietary intakes between population and hospital controls measuredby the FFQ. Materials and
Methods: A quantitative FFQ and a short food habit questionnaire (SFHQ) weredeveloped and adapted for cancer and nutritional studies. Habitual dietary intakes were assessed in 814 Chinesewomen aged 18-81 years (407 outpatients and 407 population controls) by face-to-face interview using the FFQin Shenyang, Northeast China in 2009-2010. The Goldberg formula (ratio of energy intake to basal metabolicrate, EI/BMR) was used to assess the validity of the FFQ. Correlation analyses compared the SFHQ variableswith those of the quantitative FFQ. Differences in dietary intakes between hospital and population controls wereinvestigated. Odds ratios (ORs) and 95% confidence intervals (CIs) were obtained using conditional logisticregression analyses.
Results: The partial correlation coefficients were moderate to high (0.42 to 0.80; all p<0.05)for preserved food intake, fat consumption and tea drinking variables between the SFHQ and the FFQ. Theaverage EI/BMR was 1.93 with 88.5% of subjects exceeding the Goldberg cut-off value of 1.35. Hospital controlswere comparable to population controls in consumption of 17 measured food groups and mean daily intakesof energy and selected nutrients.
Conclusions: The FFQ had reasonable validity to measure habitual dietaryintakes of Chinese women. Hospital outpatients provide a satisfactory control group for food consumption andintakes of energy and nutrients measured by the FFQ in a Chinese hospital setting.