Estudo da utilização do gráfico de controle individual e do índice de capabilidade sigma para dados não normais

Abstract

This dissertation presents a critical analysis regarding the use of some statistical methods applied to Quality in cases in which the collected data are not normally distributed. The general problem refers to the occurrence of questionable decision takings starting from the interpretation of data considered normally distributed. The primordial justification for this study is the relevance of the data analysis during its collection and handling in the industrial practice and in scientific works in the most varied levels. The main objectives of this work are: to present some examples related to the usage of control charts and six sigma capability index that may induce to doubtful conclusions due to the incorrect assumption of normality; to propose critical review proceeding to the Box-Cox and/or Johnson transformations; and, finally, to discuss the conclusions and decisions established through the comparison among the gross data originally collected, the data previously analyzed and processed and the transformed data. The methodological approach combines experimental research through the analysis of simulate data generated starting from a statistical software as well as exploratory research with case study in an industrial process of precision hole measurement.