Clinical efficacy assessment of diagnostic tests: from the standpoint of analysis of prognostic factors

The usefulness of laboratory tests has been assessed by indices such as diagnostic sensitivity, specificity and predictive values. This paper describes the means by which usefulness is evaluated by analysis of prognostic factors, including risk factors and clinical outcome of therapy. It is essential to follow appropriate research designs and to make use of appropriate statistical analyses. Some of the efficient means for analyzing prognostic values include prospective investigation, as represented by cohort studies which follow characteristics of groups for a period of time, and retrospective investigation, as represented by case-controlled studies which evaluate characteristics of groups in a retrospective manner. The appropriate method of analysis for sample data which contain time factors and a relationship between cause and outcome may be multiple logistic regression analysis. This analytical method can present the effects of each factor on a given disease by odds ratios, and can also calculate the occurrence probability of the disease for each case. For example, we analyzed the prognostic factors that govern the effects of interferon therapy on hepatitis type C. We found that the genetic type and quantity of the virus are the major prognostic factors determining the efficacy of interferon therapy, which is in good accord with previous studies. Furthermore, we were able to identify some factors which have not been recognized before. Thus, appropriate research designs not only provide new insights into therapeutic approaches but can also improve the usefulness of laboratory tests.