Gaps in practice

January/February 2011

Screening for physical inactivity in general practice

A test of diagnostic accuracy

Volume 40, No.1, January/February 2011 Pages 57-61

Tania Winzenberg

Kelly A Shaw

Background

It is unclear what is the best method of accurately identifying physically inactive patients in general practice. This study aimed to compare the performance of different methods of assessing patient physical activity levels in general practice.

Methods

Thirteen general practitioners were randomly allocated to perform either their usual assessment, or this with a Lifescripts tool, on consecutive patients. The authors measured patients’ physical activity by accelerometer over 1 week, including steps per day, then calculated agreement, kappa specificity, sensitivity, positive and negative predictive value (PV) and ROC characteristics for each assessment method (GPs’ usual assessment, Lifescripts tool and steps per day) against the reference standard of accelerometer classification.

Results

Data from 29 patients was included. Agreement between subjective assessments was highest for GPs’ usual assessment (agreement 73%; kappa 0.47; p=0.03), which also gave the highest area under the ROC curve (0.75, 95% CI: 0.52–0.98). However, this still had low specificity (67%) and positive PV (63%). Using a cut-off of 7500 steps/day maximised the area under the ROC curve at 0.91 (95% CI: 0.82–1.00), 19.2% greater than GPs’ usual assessment.

Conclusion

Measuring steps per day may be a feasible and more effective way to screen for physically inactive patients than self report. A large scale study to confirm these results is necessary.

It is recommended that healthcare providers1–5 routinely assess their patients’ physical activity (PA). However, there is limited evidence to guide general practitioners in their choice of assessment method. Currently, it is suggested that GPs assess PA from patient self report.6 Previous research by the authors has shown that self report by history taking was the method of choice for Australian GPs.7 While using self report is acceptable to GPs, it has limitations,8 including the risk of overreporting (social desirability bias) and patients finding it difficult to translate their activities into the appropriate intensity grade.7 An alternative to history taking is the use of questionnaires, but these also rely on self report, and even in the research setting such instruments vary in their effectiveness8 when compared against objective measures of physical activity such as pedometers or accelerometers.

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Correspondence afp@racgp.org.au

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