The Genetic Counseling Outcome Scale: a new patient-reported outcome measure for clinical genetics services.

The aim of this study was to develop a patient-reported outcome measure (PROM) for clinical genetics services. Previous research was used to develop a draft 84-item questionnaire, which was completed by 527 members of patient support groups. Responses were subjected to exploratory factor analysis (EFA). Parallel analysis was used to identify the number of factors to extract using oblique rotation. Twenty-four questions were selected to form the Genetic Counseling Outcome Scale (GCOS-24). Two hundred and forty-one patients completed a questionnaire pack before and after attendance at a genetics clinic that included the GCOS-24, and validated measures of health locus of control, perceived personal control, anxiety, depression, satisfaction with life and authenticity. Concurrent validity of the GCOS-24 was assessed using bivariate correlation. Sensitivity to change of the GCOS-24 was assessed using analysis of variance. EFA identified a single overarching construct consisting of seven dimensions. Internal consistency (α = 0.87) and test-retest reliability (r = 0.86) are good. The GCOS-24 shows convergent and divergent validities, and sensitivity to change over time with a medium-to-large effect size (Cohen's d = 0.70). The GCOS-24 has potential as a clinical genetics-specific PROM.