Background Simulated patient, or so-called 'mystery-shopper', studies are a controversial, but potentially useful, approach to take when conducting health services research. Aim To investigate the construct validity of survey questions relating to access to primary care included in the English GP Patient Survey. Design and setting Observational study in 41 general practices in rural, urban, and inner-city settings in the UK. Method Between May 2010 and March 2011, researchers telephoned practices at monthly intervals, simulating patients requesting routine, but prompt, appointments. Seven measures of access and appointment availability, measured from the mystery-shopper contacts, were related to seven measures of practice performance from the GP Patient Survey. Results Practices with lower access scores in the GP Patient Survey had poorer access and appointment availability for five out of seven items measured directly, when compared with practices that had higher scores. Scores on items from the national survey that related to appointment availability were significantly associated with direct measures of appointment availability. Patient-satisfaction levels and the likelihood that patients would recommend their practice were related to the availability of appointments. Patients' reports of ease of telephone access in the national survey were unrelated to three out of four measures of practice call handling, but were related to the time taken to resolve an appointment request, suggesting responders' possible confusion in answering this question. Conclusion Items relating to the accessibility of care in a the English GP patient survey have construct validity. Patients' satisfaction with their practice is not related to practice call handling, but is related to appointment availability.
