O'Reilly logo

Industrial Statistics with Minitab by Xavier Tort-Martorell Llabres, Lluis Marco Almagro, Pere Grima Cintas

Stay ahead with the world's most comprehensive technology and business learning platform.

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

Start Free Trial

No credit card required

14.5 Customizing the Study

14.5.1 Transform

When the original data are not normal, you may use a simple mathematical transformation to obtain data that, for practical purposes, are normally distributed.

nc14uf003.eps

14.5.2 Estimate

Method used to estimate the standard deviation.

nc14uf004.eps

Usually, there is no need to change the default options. The within standard deviation is estimated via the average of the sample variances (if the sample sizes differ, each variance is weighted by the degrees of freedom of each sample).

It is well known that the sample variance s2 is an unbiased estimator of the population variance σ2; however, the sample standard deviation s is not an unbiased estimator of the population standard deviation σ. To make it unbiased, it is necessary to apply a bias correction factor which is a constant that depends on the degrees of freedom used to estimate s2. Minitab applies it by default (use unbiasing constants).

When the subgroup size is one, by default the short time variability is computed via the average moving range of order two.

14.5.3 Options

nc14uf005.eps

Sometimes, 8σ is used as the width of the bell-shaped curve to compute the capability indexes.

To require Cp = 1 using 8σ as the ...

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, interactive tutorials, and more.

Start Free Trial

No credit card required