Basic concepts of measuring diet and physical activity
In this section, basic concepts which are fundamental to the measurement of diet and physical activity are discussed. Before using in a study, measurement tools should be assessed for reliability and validity in a population which is similar to the one under investigation. It is not advisable to simply lift and use a questionnaire and assume that it will be precise and accurate in any given population group. Equally any new tool or method should be tested for reproducibility, and a validation, or at least a calibration study, undertaken before it is applied in any research study.
It is important to identify the source of error in any measurement of diet or physical activity; the error may be systematic and/or random (Kipnis et al, 2001). This means investigating if the measurement error is associated with the test instrument, the administration procedures, or if it is to do with inconsistencies within the individual (Rikli, 2000). It may be possible to overcome some of the error and thus increase the reliability and validity of the measurement.
Kipnis V, Midthune D, Freedman LS, Bingham S, Schatzkin A et al
Empirical evidence of correlated biases in dietary assessment instruments and its implications
Am J Epi. 2001; 153:394-403
Reliability, validity, and methodological issues in assessing physical activity in older adults
Res Quart Exerc Sport. 2000; 71:89-96