Minimal important difference for anxiety and depression surveys after intervention to increase daily physical activity in smokers

Abstract

Nicotine dependence is associated with the presence of anxiety and depression. Several instruments (questionnaires) are used to quantify these symptoms; however, it has not been known yet which magnitude of change quantified by these instruments better reflects relevant alterations in these symptoms after an intervention in smokers. The objective of this study was to determine the value of the minimal important difference for questionnaires about anxiety and depression after an intervention aimed at increasing daily physical activity in smokers. Fifty-seven smokers with normal spirometry underwent a program to increase daily physical activity. During the two-month period, they used a pedometer (step counter) and received an informative booklet, both as incentives to increase daily physical activity. Participants were assessed pre- and post-program and, in each assessment, questionnaires that quantify anxiety and depression were applied (Hospital Anxiety and Depression Scale - HADS A and D; State-Trait Anxiety Inventory - STAI, and Beck Depression Inventory - BDI). There was a significant increase in daily physical activity (steps/day) and an improvement in the scores of all questionnaires. Minimal important difference values for this population were eight points for the HADS A, six for HADS D, ten for STAI and 11 for BDI. The present study allowed to determine the minimal important difference values for reduction of anxiety and depression after a support program to increase daily physical activity in smokers. These results indicate a potentially significant change, beyond any measurement error.