Methods and formulas for graphs in Nonnormal Capability Sixpack

The histogram is displayed with a distribution curve that is generated using specified or maximum likelihood estimates of the parameters of the distribution used in the nonnormal capability analysis.

For information on the calculations used to create the probability plots, go to Methods for Individual Distribution Identification.

For nonnormal capability sixpack, Minitab displays different control charts depending on the subgroup size.

• If the subgroup size is 1, Minitab displays an I-MR chart. To calculate the control limits in this case, Minitab estimates the probability density function from the data and uses this function to calculate the 0.135th and 99.865th percentiles. The values that correspond to these percentiles represent the lower and upper control limits.
• If the subgroup size is greater than 1, Minitab displays an Xbar chart with an R or S chart.

  For information on the methods used for the Xbar chart, go to Methods and formulas for Xbar Chart.

  For information on the methods used for the R chart, go to Methods and formulas for the R chart in Xbar-R Chart.

  For information on the methods used for the S chart, go to Methods and formulas for the S chart in Xbar-S Chart.