Measuring Posttraumatic Growth and Depreciation After Spinal Cord Injury: A Rasch Analysis

Purpose: Individuals with spinal cord injury (SCI) may experience both positive (posttraumatic growth, PTG) and negative (posttraumatic depreciation, PTD) psychological changes following the injury. PTG and PTD were assessed using the 10-item short form of the Posttraumatic Growth Inventory (PTGI-SF) and 10 matched negatively worded items for PTD (selected from the PTGI-42) within the Swiss Spinal Cord Injury Cohort Study (SwiSCI). This item selection is henceforth called PTG/D-SF. The objective of this study was to test the metric properties of the PTG/D-SF to determine the best strategy to derive reliable sum scores and to test the validity of several different structural conceptualizations. Method: Using cross-sectional data (N = 278), a series of unidimensional and multidimensional Rasch analyses of the PTG/D-SF (N = 20) were performed. Rasch analyses were conducted separately for the items or by domains to investigate dimensionality, monotonicity, item and model fit, and local item dependency of the instrument. Results: The separate PTG and PTD items or their domains can be summated to form a unidimensional scale. Aggregation into domains improved the score distribution and increased the scope of the instruments. The reliability of the sum score for PTG was good (Person Separation: 0.81); the one for PTD was admissible (Person Separation: 0.77). Conclusion: PTG and PTD should be understood as distinct constructs rather than two ends of a continuum. Findings support the use of a PTG total score and to some degree the PTD total score. Future work could adapt the PTD items to improve the performance of the scale. Impact and Implications The current study is the first to examine the metric properties and dimensionality of a measure for posttraumatic growth (PTG) and depreciation (PTD) in spinal cord injury using modern test theory. Higher reliability is achieved with a separate scoring of the PTG and PTD dimensions, which therefore must be understood as two distinct constructs. Clinicians and rehabilitation professionals should monitor in parallel, both positive and negative perceived life changes after the onset of a spinal cord injury. Both PTG and PTD items can be aggregated into overall sum scores and meaningfully interpreted, although the measurement precision of the PTG sum score can be expected to be higher than the one of the PTD sum score.