Options for Evaluating Treatment Benefit in MCI and Prodromal Alzheimer’s Disease: Content Validity of the Perceived Deficits Questionnaire (PDQ) in Patients with Early Symptoms of Cognitive Decline

Background: Many instruments used to assess outcomes of treatment for Alzheimer’s disease (AD) have no published evidence of their relevance and content validity in earlier stages of the disease, i.e., mild cognitive impairment, or prodromal AD (pAD). The objective of this project was to evaluate the applicability and usefulness of the Perceived Deficits Questionnaire (PDQ) as an outcome measure in this population using qualitative methodology to support content validity. Method: Two waves of qualitative interviews were conducted in patients with MCI and pAD. Results: Evidence for content validity and usefulness of the instrument was demonstrated in the patient interviews. Minor modifications to the wording of several items were suggested for the PDQ and the recall period was changed. Conclusion: With these modifications, the PDQ has improved content validity and relevance. It is therefore a potentially useful outcome measure to evaluate therapeutic benefit in interventional studies of patients in the early stages of AD.