Statistics::SPC - Calculations for Stastical Process Control

Creates thresholds based on the variability of all data, # of samples not meeting spec, and variablity within sample sets, all from training data.

Note: this is only accurate for data which is normally distributed when the process is under control

Recommended usage: at least 15 sample sets, w/ sample size >=2 (5 is good) This module is fudged to work for sample size 1, but it's a better idea to use >= 2

Important: the closer the process your are monitoring to how you would like it to be running (steady state), the better the calculated control limits will be.

Example: we take 5 recordings of the CPU utilization at random intervals over the course of a minute. We do this for 15 minutes, keeping all fifteen samples. Using this will be able to tell whether or not CPU use is in steady state.

 my $spc = new Statistics::SPC;
 $spc->n(5) # set the number of samples per set
 $spc->Uspec(.50); # CPU should not be above 50% utilization
 $spc->Lspec(.05); # CPU should not be below 5%
 	# (0 is boring in an example)

 # Now feed training data into our object
 $return = $spc->history($history); # "train the system";
 	# $history is ref to 2d array;
 	# $return > 1 means process not likely to
 	# meet the constraints of your specified
 	# upper and lower bounds

 # now check to see if the the latest sample of CPU util indicates
 	# CPU utilization was under control during the time of the sample

 $return = $spc->test($data); # check one sample of size n
 	# $return < 0 there is something wrong with your data
 	# $return == 0 the sample is "in control"
 	# $return > 0 there are $return problems with the sample set

The range of the data ($self->R) greater than our calculated upper limit on the intra-sample range ($self->UCLR);

The range of the data ($self->R) less than our calculated lower limit on the intra-sample range ($self->LCLR);

The average of the sample set ($self->Xbar) is greater than our calculated upper limit ($self->UCLXbar)

The average of the sample set ($self->Xbar) is less than our calculated upper limit ($self->LCLXbar)

The number of data that fall outside our specification (i.e. errors) ($self->p) is greater than our calculated upate limit ($self->UCLp)

The number of data that fall outside our specification (i.e. errors) ($self->p) is less than our calculated upate limit ($self->LCLp)

Erich S. Morisse <emorisse@cpan.org>

Copyright (c) 2007 Erich Morisse

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

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