# Validity, reliability, responsiveness and interpretability of the EFAS-DK PROM: an observational cohort study of Danish speaking foot and ankle patients

## TL;DR

The EFAS-DK questionnaire is a valid and reliable tool for measuring outcomes in Danish-speaking foot and ankle surgery patients.

## Contribution

This study validates the EFAS-DK PROM for Danish-speaking patients, confirming its clinical usefulness and cross-border comparability.

## Key findings

- EFAS-DK demonstrated high internal consistency (Cronbach’s alpha 0.88) and test-retest reliability (ICC 0.93).
- The questionnaire detected a clinically relevant change score of 6, representing 25% of the total scale.
- Control group scores showed no significant changes, confirming the questionnaire's ability to differentiate patient outcomes.

## Abstract

This study is an external evaluation of the Patient Reported Outcome Measure (PROM) EFAS-DK developed by the European Foot and Ankle Society (EFAS). The evaluation included a test of the psychometric properties.

From October 2019 to September 2022, 101 patients undergoing elective foot or ankle surgery completed questionnaires (EFAS-DK, SEFAS-DK, EQ-5D-5L) prior to surgery and 6 months post-surgery. A subgroup of patients completed a retest. A foot-healthy group control group was added. Testing covered construct validity with hypothesis testing, floor and ceiling effects, internal consistency (Cronbach’s Alpha), test-retest reliability (ICC 2.1), effect size (ES), Standardized Response Mean (SRM), Smallest Detectable Change (SDC) and Minimal Important Change (MIC).

Moderate construct validity with 59% confirmed hypothesis. High content validity, no floor ceiling effects. Cronbach’s alpha 0.88, ICC 0.93. ES and SRM were both 1.06. SDC 4 and MIC 6. Control group score changes was insignificant.

EFAS-DK is a valid, reliable, and responsive foot and ankle PROM score. EFAS-DK can detect a clinically subjective relevant change score of 6 (25% of the total scale), which makes it useful for implementation in the clinic when evaluating patients undergoing foot and ankle surgery. Comparison with a control group showed results that significantly differ from the patients.

IIa prospective observational analytic cohort study.

This study is a validation of a Patient Reported Outcome Measure (PROM) called the EFAS-DK. PROM questionnaires captures a health condition of a patient at a given time without any interpretation of the response by the health professional. PROMs are becoming more widespread in the evaluation of surgical treatments because the treatment effect is best evaluated by the patient themself. EFAS-DK is the Danish version of the EFAS Score, a PROM with the intention to be used globally targeting patients undergoing foot or ankle surgery. The validation process of a PROM intended for clinical use is essential and must be based on the target patient group. A valid PROM must be truthful, reliable and be able to detect relevant score changes. We tested a questionnaire on patients before and after surgery and compared with healthy individuals at similar time intervals. Answers were converted to points and underwent statistical analysis and the questionnaire demonstrated satisfactory results in all aspects of a thorough validation (validity, reliability, responsiveness, and interpretability). With this validated Danish version, we add an acknowledged PROM to clinical daily use for evaluation of foot and ankle patients. Furthermore, it is possible to compare data across borders for scientific purposes.