OBSERVATIONAL DATA-BASES IN NEUROLOGICAL DISORDERS - SELECTION BIAS AND GENERALIZATION OF RESULTS

Observational data bases in the neurological disorders may be an impor tant source of information on etiology and natural history. The abilit y to make valid generalizations of results from a data base to the gen eral population of patients with a particular disorder is not, however , guaranteed. The design or analysis of the study may result in select ion biases that make inferences untenable. Examples are presented whic h demonstrate the potential for bias limiting the validity of inferenc es beyond the sample observed.