The timing and method of administration of questionnaires affects the way patients evaluate services, the findings of a UK study suggest.

Researchers reviewed the GMC's Patient Questionnaire, which could be used in revalidation. They found that differences in data collection methods, such as whether an exit survey or postal survey was used, led to variations in the way patients viewed services.

Postal responses were more critical of doctors' performance than exit surveys, they found.

Writing in the journal Primary Health Care Research and Development, the Exeter University researchers said there may be several reasons for this.

One explanation could be that patients filling in a survey in their own home feel less inhibited about providing a critical assessment than those completing a questionnaire in a surgery waiting room.

The researchers also found a touch-tone telephone approach was prone to bias because of substantially higher non-response rates.

The findings suggested that an exit survey was the best method of assessing patients' views of consultations, they said.

The researchers said: 'Caution is required towards mixing administration methods when creating and applying benchmarks against which a doctor's performance is assessed until further research is undertaken.'

They added: 'This is of particular importance should such patient questionnaires become a routine component of multi-source feedback in the UK's current plans for the revalidation of doctors.'

• Primary Health Care Research and Development Online 2010