Categorical answer modes provide superior validity to open answers when asking for level of physical activity: A cross-sectional study

Aims: Physical activity (PA) used as prevention and treatment of disease has created a need for effective tools for measuring patients' PA level. Our aim was therefore to assess the validity of two PA questions and their three associated answer modes.

Methods: Data on PA according to the PA questions and Actigraph GT3X+ accelerometers, aerobic fitness (VO(2)max), cardiovascular biomarkers, and self-rated general health were collected in 365 Swedish adults (21-66 years). The PA questions ask about weekly PA via categories (Categorical), an open-ended answer (Open), or specified day by day (Table).

Results: The Categorical mode, compared with the Open mode, correlated (Spearman's rho) significantly more strongly (p<0.05) with accelerometer PA (0.31 vs. 0.18) and VO(2)max (0.27 vs. 0.06), and the level of BMI (-0.20 vs. -0.02), waist circumference (-0.22 vs. -0.03), diastolic blood pressure (-0.16 vs. 0.08), glucose (-0.18 vs. 0.04), triglycerides (-0.31 vs. -0.07), and general health (0.35 vs. 0.19). The validity of the Categorical and Table modes were similar regarding VO(2)max and accelerometry, but the Categorical mode exhibited more significant and stronger correlations with cardiovascular biomarkers. The capacity of the PA questions to identify insufficiently physically active individuals ranged from 0.57 to 0.76 for sensitivity and from 0.47 to 0.79 for specificity.

Conclusions: The Categorical mode exhibits the strongest validity and Open mode the weakest. The PA questions may be used on a population level, or as a tool for determining patents' appropriateness for treatment.