No study in medical science is complete without application of the statistical principles. Incorrect application of statistical tests causes incorrect interpretation of the study results obtained through hard work. Yet statistics remains one of the most neglected and loathed areas, probably due to the lack of understanding of the basic principles. In microbiology, rapid progress is being made in the field of diagnostic test, and a huge number of studies being conducted are related to the evaluation of these tests. Therefore, a good knowledge of statistical principles will aid a microbiologist to plan, conduct and interpret the result. The initial part of this review discusses the study designs, types of variables, principles of sampling, calculation of sample size, types of errors and power of the study. Subsequently, description of the performance characteristics of a diagnostic test, receiver operator characteristic curve and tests of significance are explained. Lack of a perfect gold standard test against which our test is being compared can hamper the study results; thus, it becomes essential to apply the remedial measures described here. Rapid computerisation has made statistical calculations much simpler, obviating the need for the routine researcher to rote learn the derivations and apply the complex formulae. Thus, greater focus has been laid on developing an understanding of principles. Finally, it should be kept in mind that a diagnostic test may show exemplary statistical results, yet it may not be useful in the routine laboratory or in the field; thus, its operational characteristics are as important as the statistical results.
