Pediatric spinal cord injury in Sweden; how to identify a cohort of rare events

Study design: Register study enhanced and verified by medical records and personal interviews and examinations. Settings: Sweden. Objectives: To define a method of identifying a study population of rare events. To point out the relative importance of every step, an example is given of identifying persons who sustained traumatic spinal cord injury (SCI) in childhood. Methods: Cases were identified in seven steps that all needed to be fulfilled, from definition of selection criteria through combination of several data sources, to the use of several verification methods. Results: Initial screening by registers identified 384 possible cases, which however were found by subsequent analysis to include a large number of incorrect cases. At completion of all analytic steps, 35 living cases could be fully verified and 14 deceased cases could be partially verified. Conclusions: Registers offer a practical initial source for study population identification. The screening of International Classification of Diseases codes de. ning SCI only included less than 30% of 'true' SCIs. Subsequently, further refinement and quality control is necessary in order to ensure validity. Such further verification is time-consuming, but nevertheless necessary in order to verify a true cohort.