Goal attainment scaling: a direct comparison of alternative rating methods

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Abstract
Purpose: To compare two alternative rating systems for goal attainment scaling (GAS) intended to improve capture of goal underachievement. Setting: A tertiary inpatient neurorehabilitation unit. Design: Secondary comparative analysis of prospective cohort data. Participants: A total of 243 patients were included, with 977 goals between them; M:F ratio 146:97, mean age 44.8 (SD 14.2) years. Diagnosis: 200 (82%) acquired brain injury, 21 (9%) spinal cord injury, 22 (9%) other neurological conditions. Methods: Goal attainment scaling-rated achievement of 1—6 patient-selected goals was collected using the standard 5-point scale (—2 to +2) and formula to derive aggregated T-scores, as recommended by its originators. Two alternative 6-point rating systems were applied retrospectively. Version 1 set all baseline scores at ‘—2’ and added ‘—3’ to denote ‘worsening’. Version 2 added a ‘—0.5’ score to denote ‘partial achievement’ for goals starting at ‘—1’, without change to range or baseline scores. Results: Baseline scores were identical for standard rating and version 2 (median 34.9, interquartile range (IQR) 31.9—35.5), but lower for version 1 (median 21.0, IQR 19.8—22.6), which was reflected in the change scores. While median achieved T-scores were 50.0 for all three methods, version 2 marginally overestimated goal attainment (Wilcoxon z —6.8, P<0.001), while version 1 underestimated it (Wilcoxon z —7.2, P<0.001), in comparison with standard goal rating. Conclusion: Different goal rating methods may have significant impact on goal attainment scaling results. Version 2 provided the closest match to standard rating, supporting documentation of partial goal achievement without affecting score range. For analysis and reporting, ‘0.5’ scores should be converted to ‘—1’, to maintain parity with standard rating systems.

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