|Contribution title||Reducing attrition through vital status tracing in spinal cord injured patients: Evidence from the Swiss Spinal Cord Injury (SwiSCI) cohort study|
|Form of presentation||Poster|
Introduction: Attrition, or loss to follow-up (LTFU), in longitudinal studies can result in selection bias and hinder study validity. Previous research on attrition in chronic disease populations have suggested attrition to be associated with an increased risk of mortality. Spinal cord injuries (SCI) are a chronic disease with evidenced reductions in life expectancy and increased premature mortality. Given the potential impact of attrition for this population, a comprehensive tracing strategy was undertaken to ascertain and update the vital status (VS) of persons included in the Swiss Spinal Cord Injury (SwiSCI) cohort study.
Methods: Vital status of persons with SCI was updated through medical records of SwiSCI-covered specialized rehabilitation centers and, where-needed, tracing through Swiss municipalities. Loss to clinic (LTC) and loss to follow-up (LTFU) were defined as having no available VS information 18 months before the population censoring date (September 30, 2011), with the latter involving the additional tracing through one or more municipalities. For certain cases, municipalities were contacted without first checking medical records due to practicality issues (e.g., historical, paper-based records). Risk factors for LTFU were assessed using logistic regression, conditional on being LTC.
Results: 3’270 individuals were included in the vital status update. 1’041 individuals were LTC and required additional tracing through municipalities. Among those with an identified VS (N=889), 336 had died by the cut-off date. Preliminary results suggest that risk of LTFU increases with increasing time since LTC and decreases with age. Stratified analysis suggest an increased risk for LTFU among younger women. For the 1’368 cases that were traced directly through municipalities, VS could be updated for 75.8% of these cases, with 546 (52.7%) deaths.
Conclusion: Results from this study can help to inform the extent of potential LTFU-bias on mortality and will therefore facilitate the correction of mortality and life expectancy estimates in future analyses. Tracing through municipalities is an effective follow-up methodology that could be applicable for other chronic disease cohorts to reduce attrition-related bias.