DIFFERENTIAL POSTMORBIDITY MORTALITY IN OBSERVATIONAL STUDIES OF RISK-FACTORS FOR NEUROLOGIC DISORDERS

Selection bias may be introduced in case-control or cross-sectional st udies, and the impact on the observed associations may be dramatic. Ma ny authors have examined this issue primarily in the context of subjec t source (e.g. referral bias). The potential bias encountered when a r isk factor associated with outcome is also associated with an increase in mortality among cases greater than that among those not developing the disease (e.g. selective survival) is examined here. The potential for selective survival bias arising in observational studies is demon strated in studies of the etiology of neonatal seizures and Parkinson' s disease.