The validation of physical activity instruments for measuring energy expenditure: problems and pitfalls

Objective: To review and categorize the problems associated with undertaking physical activity validation studies and to construct a checklist against which any study could be compared. Results: The studies reviewed demonstrated problems in defining the dimension of physical activity that is of interest and in the selection of an appropriate comparison technique. Ideally this should be closely related to the true exposure of interest and assess that exposure objectively and without correlated error from the study instrument in question. In many studies inappropriate comparison methods have been chosen which do not measure the true underlying exposure and which are likely to have correlated error. The choice of study populations, the frame of reference of the exposure measurement and the use of appropriate statistical methods are also problematic areas. Conclusions: There is no ideal measurement instrument or validation study design that is suitable for all situations. However, the checklist in this paper provides a means whereby the appropriateness of studies already undertaken or at the planning stage can be assessed.