Six Sigma Green Belt Certification Practice Exam

What formula represents the P/T ratio?

1. 6*standard deviation / (USL - LSL)

2. (Product Variation + Measurement Variation) / 6*standard deviation

3. (USL - LSL) / 6*standard deviation

4. 6*standard deviation / (Product Variation + Measurement Variation)

The correct answer is: 6*standard deviation / (USL - LSL)

The P/T ratio, or Process Tolerance ratio, is a crucial measure in quality management that examines the spread of the process distribution relative to its allowable tolerance range. The correct formulation of this ratio is found in the option you selected: (USL - LSL) / 6*standard deviation. The rationale behind this formula is that it calculates how many standard deviations fit within the difference between the upper specification limit (USL) and lower specification limit (LSL). The factor of 6 in the formula accounts for the total range covered by the normal distribution for approximately 99.73% of the data (three standard deviations on either side of the mean), which is essential in determining the capability of a process. When using this ratio, a higher value indicates a more capable process, as it suggests that the variation in the process (represented by the standard deviation) is small relative to the allowable width of the specifications. This ratio helps organizations determine whether their processes can consistently produce products within specification limits. In the context of the incorrect options, they do not accurately represent the relationship between process variation and specification limits, which is central to the definition of the P/T ratio. The incorrect choices either misrepresent the necessary calculations or introduce unnecessary components