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Introduction
There is a paucity of critical studies on Six Sigma beyond that of "how to" and that of descriptive accounts, with a focus on measures and results ([21] McAdam and Lafferty, 2004). [2] Anbari and Kwak (2004) confirmed that integrating the data-driven, structured Six Sigma processes into organizations has room for improvement. While recognizing the need for improvements in Six Sigma, some researchers suggested improving it using different technical approaches ([32] Siviy et al. , 2005; [16] Goh and Xie, 2004).
A deeper scarcity of studies that compare and contrast Six Sigma with Critical Thinking, CT, exists as well. In fact, when Emerald search engine was used to locate papers tackling the term "Six Sigma" and the term "Critical Thinking" concurrently in all fields excluding text, surprisingly, zero papers were produced. This lack of research that combines Six Sigma and CT became more evident when two other search engines, EBSCO and Proquest, rendered zero papers critiquing Six Sigma in contrast with CT. This dearth of such research can be attributed to the fact that Six Sigma was born and raised in the field by practitioners. Indeed, Motorola was the first company to launch Six Sigma initiatives in 1986 ([28] Rancour and McCracken, 2000). Consequently, researchers focused on Six Sigma's statistical aspects, implementations, benefits, and methodologies. As a result, an opportunity for a research to fundamentally improve Six Sigma does exist; such research may provide insights to the reasons some organizations experience great deal of success while others experience disappointments with process improvement initiatives.
Six Sigma, 5 Whys, and Critical Thinking
Six Sigma has been defined as "an organized and systematic method for strategic process improvement and new product and service development that relies on statistical methods and the scientific method to make dramatic reductions in the customer defined defect rates" ([20] Linderman et al. , 2003). From the statistical perspective, the term Six Sigma is defined by convention as having less than 3.4 defects per million opportunities (DPMO) or a success rate of 99.9997 percent, where the term sigma is used to represent the variation about the process average ([3] Anthony and Banuelas, 2002). Motorola confirms that Six-Sigma was invented by them in 1986 as a metric for measuring defects and improving quality...