Comparing the nine-item Shared Decision-Making Questionnaire to the OPTION Scale - an attempt to establish convergent validity

BACKGROUND: While there has been a clear move towards shared decision-making (SDM) in the last few years, the measurement of SDM-related constructs remains challenging. There has been a call for further psychometric testing of known scales, especially regarding validity aspects.

OBJECTIVE: To test convergent validity of the nine-item Shared Decision-Making Questionnaire (SDM-Q-9) by comparing it to the OPTION Scale.

DESIGN: Cross-sectional study.

SETTING AND PARTICIPANTS: Data were collected in outpatient care practices. Patients suffering from chronic diseases and facing a medical decision were included in the study.

METHODS: Consultations were evaluated using the OPTION Scale. Patients completed the SDM-Q-9 after the consultation. First, the internal consistency of both scales and the inter-rater reliability of the OPTION Scale were calculated. To analyse the convergent validity of the SDM-Q-9, correlation between the patient (SDM-Q-9) and expert ratings (OPTION Scale) was calculated.

RESULTS: A total of 21 physicians provided analysable data of consultations with 63 patients. Analyses revealed good internal consistency of the SDM-Q-9 and limited internal consistency of the OPTION Scale. Inter-rater reliability of the latter was less than optimal. Association between the total scores of both instruments was weak with a Spearman correlation of r = 0.19 and did not reach statistical significance.

DISCUSSION: By the use of the OPTION Scale convergent validity of the SDM-Q-9 could not be established. Several possible explanations for this result are discussed.

CONCLUSION: This study shows that the measurement of SDM remains challenging.