Análise crítica da aplicação de métodos estatísticos em processos definidos por dados que não apresentam distribuição normal

Abstract

This paper presents a critical analysis regarding the use of specific “quality tools” and some methods applied to Production Engineering when the collected data are not normally distributed. The general problem refers to the occurrence of questionable decisions starting from the interpretation of data considered “normally distributed”. The primary justification for this study is the relevance of the data analysis during their collection and the handling of scientific works in the most varied levels. The main objectives of this paper are: to present some examples related to the Statistical Process Control and the Six Sigma Methodology, which may induce to doubtful conclusions due to the incorrect assumption of normality; to propose critical review proceedings to the Box-Cox and/or Johnson transformations; finally, to discuss the conclusions and decisions established through the comparison among the originally collected and the transformed data. Keywords: Statistical Methods; Non-normal Data; Data Transformation.