Reproducibility and Validity of a Semi-Quantitative Food Frequency Questionnaire for Assessing Dietary Intake of Vegetarians and Omnivores in Harbin, China

This study aims to evaluate the reproducibility and validity of a semi-quantitative food frequency questionnaire (SQFFQ) developed for vegetarians and omnivores in Harbin, China. Participants (36 vegetarians and 64 omnivores) administered SQFFQ at baseline (SQFFQ1) and six months later (SQFFQ2) to assess the reproducibility. The 24 h recalls (24 HRs) for three consecutive days were completed between the administrations of two SQFFQs to determine the validity. For reproducibility, Pearson correlation coefficients between SQFFQ1 and SQFFQ2 for vegetarians and omnivores were 0.45 similar to 0.88 and 0.44 similar to 0.84, respectively. For validity, unadjusted Pearson correlation coefficients were 0.46 similar to 0.83 with an average of 0.63 and 0.43 similar to 0.86 with an average of 0.61, respectively; energy-adjusted Pearson correlation coefficients were 0.43 similar to 0.82 with an average of 0.61 and 0.40 similar to 0.85 with an average of 0.59, respectively. Majority of the correlation coefficients for food groups and macronutrients decreased or remained unchanged after energy adjustment. Furthermore, all correlations were statistically significant (p < 0.05). Bland-Altman plots also showed reasonably acceptable agreement between the two methods. In conclusion, the SQFFQ developed in this study has reasonably acceptable reproducibility and validity.