Ensuring face validity in patient-related outcome scores--a matter of content

Patient reported outcome (PRO) questionnaires are increasingly used to measure treatment effect in patients with knee pathology. PROs commonly used to assess outcome in patients with knee conditions can be generic, knee-specific, or condition-specific. Most PROs have been created based on clinician-based consensus and are not patient-centered. Items (questions plus their response options) in PROs can be generated by clinicians or through patient interviews. Items created by clinicians possess face validity. The objective of this study was to find all existing PRO items with potentially relevant content for patients with knee pathology.

An exhaustive literature search was conducted for PRO questionnaires in English, German, and Scandinavian languages used to assess outcome in patients with knee pathology. The items from the collected PROs were assessed for content redundancy and item reduction was carried out to isolate items of unique content. These items were grouped into one of the components of the ICF classification system.

Thirty-one PROs used for assessment of patients with knee problems were identified, yielding 539 items. Approximately 70% of these items consisted of redundant content matter. The item pool was reduced to a pool of 157 items.

The search yielded 157 items of unique content.

The identified items can be used to build condition-specific PRO questionnaires for patients with knee pathology.