A review of the methods used by studies of dietary measurement.

Studying the association between diet and disease requires reliable and valid methods for the assessment of diet. The authors reviewed the literature concerned with the assessment of these aspects of the measurement of dietary intake. Studies were examined for the stated purpose and scope of the dietary instrument, for a description of the instrument itself, for any methods employed to train individuals in its use and for the methods used to assess its reliability and validity. Of the 59 studies reviewed, 54% described fully the dietary method used. Of the 39 studies that described the results using questionnaires, 51% gave specific information on questions asked and only 18% included the questionnaire itself. Reliability was assessed in 26 studies and 74% (19) used the test-retest reliability and 22% (6) used proxies to assess reliability. Validity was assessed in 46 studies and 83% (38) used indirect methods that compared the results of one dietary method (e.g. 24 hr recall) with another more extensive one (e.g. diet history). Thirty five percent (16) used biochemical and 15% (7) used other methods. This review suggests several directions that might be usefully followed in conducting and reporting further research in the development of methods to assess diet.