USE OF POWER ANALYSIS IN CHOOSING APPROPRIATE SAMPLE SIZE FOR QUALITY INSPECTION

Selection of an appropriate sample size is one of the most important aspects of any quality inspection. Th e right sample size enables making valid conclusions about the quality of the product with minimum necessary resources. Th e choice of sample size and the probability of Type II error (ß) are closely connected. Th e purpose of this paper is to examine how usage of a statistical power analysis can improve researcher's decision about choosing an appropriate sample size for experimental purposes and quality inspection.Apart from sample size, the power of a study (1-ß) or the probability that the study will yield signifi cant results is determined by the magnitude of the treatment eff ect and by the level of statistical signifi cance required (α).Th e goal of power analysis is to balance values of these three factors to get an appropriate power.Impact of individual changes of each factor on the power was observed through a hypothetical statistical example based on a signifi cance test in which the diff erence between proportions of two independent samples was estimated.Power and Precision soft ware was used for calculations.Results of the power analysis have shown that increase in eff ect size, sample size and/or level of statistical signifi cance lead to an increase in power.Th is means if power increased and/or eff ect size and/or level of statistical signifi cance decreased, a larger sample size would be required.