The National Head and Spinal Cord Injury Survey: design and methodology.

The National Head and Spinal Cord Injury Survey was designed to provide statistics that measure the morbidity and economic costs of injury to the head or spinal cord for the population in the contiguous United States for the year 1974. This article described the multistage design that was used for sampling in the survey, and includes general remarks on random and probability sampling. The criteria for eligibility for the survey and the methodology for data collection are also discussed. It is necessary to understand these aspects of the survey in order to interpret the findings.