Essentials of Biostatistics. 9. Statistical inference from qualitative data: proportions, relative risks and odds ratios

Abstract

Earlier in this series(1) we used the terms qualitative and quantitative for different types of data. Inference for the latter will be discussed in the next Article. This Article is restricted to the qualitative data. These include all those that are summarized in terms of proportions or rates and ratios. For example, systolic blood pressure is quantitative but becomes qualitative for our purpose when divided into categories such as < 120, 120-139 and 140 +. This occurs when the interest is in the proportion of subjects falling into these categories rather than in mean. A large number of statistical methods are available for different situations of this type of data but we include those in this Article that are commonly used in health and medicine. Methods of inference from proportions in one variable setup are given in Section 9.1. Sections 9.2 and 9.3 are devoted to inference on proportions in two-variable setup from independent and paired samples, respectively. Inference on relative risks and odds ratios is included in Section 9.4.