Evaluation of reliability and validity of the General Practice Physical Activity Questionnaire (GPPAQ) in 60-74 year old primary care patients.

Background: GPPAQ (General Practice Physical Activity Questionnaire) is a self-assessment physical activity questionnaire widely used in primary care. Reliability and validity data in older people are lacking. The study aims were: to assess GPPAQ's reliability and validity in 60-74 year olds from the PACE-Lift (Pedometer Accelerometer Consultation Evaluation-Lift) physical activity trial; and to assess whether adding brisk walking to the GPPAQ score improves its validity when assessing if physical activity guidelines are being met.

Method: Physical activity was assessed objectively by accelerometry and by self-report GPPAQ over one week periods at baseline, and three and twelve months later, in 60-74 year old participants from three United Kingdom general practices enrolled in PACE-Lift. Reliability: GPPAQ scores in controls (n = 148) were compared for repeatability at baseline, 3 and 12 months.

Validity: we compared the GPPAQ "active" rating (those not requiring physical activity advice) with those achieving physical activity guidelines using accelerometry, in all baseline subjects (n = 298). Using accelerometry as an objective comparator, GPPAQ sensitivity and specificity were calculated and repeated after adding brisk walking into the GPPAQ score (GPPAQ-WALK).

Results: For reliability, GPPAQ showed 56 % (70/126) and 67 % (87/129) of controls scored the same at 3 and 12 months respectively, as they scored at baseline. At baseline 24 % (69/289) achieved physical activity guidelines according to accelerometry, whilst 16 % (47/289) were classified as GPPAQ "active". GPPAQ had 19 % (13/69) sensitivity and 85 % (186/220) specificity. GPPAQ-WALK had 39 % (27/69) sensitivity and 70 % (155/220) specificity.

Conclusions: GPPAQ has reasonable reliability but results from this study measuring validity in older adults indicates poor agreement with objective accelerometry for accurately identifying physical activity levels. Including brisk walking in GPPAQ increased sensitivity, but reduced specificity and did not improve overall screening performance. GPPAQ's use in National Health Service health checks in primary care in this age group cannot therefore be supported by this validity study comparing to accelerometry.