Statististical control tests based on Standard deviations

Cochran’s statistic C: Cochranwhere smax is the largest standard deviation amongst the si.
Mandel’s k-statistic Mandel-kPlot values for kij in the order of measurements made (by laboratory, e.g) and grouped by level. Draw in limits for 1% resp 5%.
Range- (R-)diagram Plot values of the sample range, R (= xmax – xmin), against time. Action limits lie at k3srWarning limits lie at + k2sr
F-test Fstatfor the new (n) resp. old (o) measurements.Compare F with Fmax for a certain number of number of degrees of freedom (= j + k – 2) and confidence level, which can be obtained from a table of overprocent points for the F-distribution (95%) resp. (99%).
Process capability Cpkwhere UTL resp. LTL are the upper and lower tolerance limits, and PS is the process scatter, sp.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: