SOME PROBLEMS IN THE ANALYSIS OF MORBIDITY DATA.

Abstract Morbidity data have increasingly been used in evaluating and comparing the health of populations. The collection of morbidity data involves a variety of methodological problems which lead to difficulties in the analysis of these data. Failure to understand the methodological issues, therefore, may lead to misinterpretation of morbidity data or to the derivation of incorrect implications. One of the key problems in the collection of morbidity data involves the adequacy of reporting. Although various methodological studies have found demographic differences in reporting accuracy, these findings have not been consistent from one study to another. However, all of the methodological studies appear to support the general principle that accurate reporting occurs when the illness in question is salient, and social and psychological barriers to reporting are absent. Degree of saliency is inferred from the following distinctions which are related to quality of reporting: self reports vs. proxy reports; conditions requiring single physician consultation vs. conditions requiring more attention; short vs. long hospital stays; episodes involving surgery vs. those not involving surgery; and the length of time for which recall is required. Attempts to link illness attitudes and behavior to quality of reporting are rare. Data are presented from a study of over 600 college students which support the idea that the orientations to symptoms and medical care have some relevance for the adequacy of reporting in morbidity surveys. The data show that among students with low illness behavior inclinations and high utilization of medical facilities, there is a clear tendency to underreport utilization experiences. The problem of response tendencies is discussed, drawing on data from morbidity studies in the Eastern Health District of Baltimore and Madison, Wisconsin. These studies illustrate the difficulties of correlating morbidity data provided by one respondent for a number of members of her family. In the usual case where independent data are not available, frequently observed correlations between psychoneurotic symptoms and illness in general may reflect a relationship between psychoneurosis and reporting tendencies or sensitivity to symptomatology, rather than a true etiological relationship. The use of illness logs is discussed as a device to eliminate problems in reporting associated with the length of the recall period. Some of the problems of recording mild symptoms and illness (and the possibility of producing them in the recording process) are discussed. The need to consider the relative importance of the errors of either overestimating or underestimating illness in terms of the purpose of the analysis is emphasized. Finally, the criteria defining morbidity in the National Health Survey are discussed in relation to the introduction of possible biases. It is argued that the criterion of action used may produce overrepresentations of various social groups in morbidity statistics which underestimate particular social trends. The importance of methodological investigations of morbidity analyses is emphasized.