Conditions for patientcompleted questionnaires

There may be certain situations where not using proxies would result in insufficient or very incomplete data. An example might be a trial in patients with brain tumours where patients who are deteriorating may become too confused, or otherwise impaired, to complete questionnaires, but the collection of data at this stage in their disease is likely to be very important. This is probably the strongest justification for asking a proxy (for example the spouse or other close relative or friend) to complete questionnaires on behalf of the patient. However, studies have suggested that the magnitude of disagreement between patients and proxies increases with the level of impairment reported by the patient, thus when the need for proxies is most salient, the most unreliable ratings are likely to be obtained. Therefore a better option would be for the patient and the proxy to complete questionnaires in parallel for as long as possible. This would give both a between-treatment comparison based on proxy and patient recording, permit an estimation of the difference between patient and proxy recording, and it might be possible to extrapolate the patient's recording forward when only the proxy was completing the forms [19].

In summary therefore, if proxies are to be used this must be part of the trial design as it is important that proxies are used throughout the trial and not only if and when the patient becomes incapable of completing, or unwilling to complete, the questionnaires themselves.

Thus, although the ideal may be to obtain the patient's own recording of their QL, there may be many practical difficulties, aspects of which may need to be considered before starting the trial.

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