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POStatistical Process Control Charts in SQL Server 2008 R2
 

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  1. POStatistical Process Control Charts in SQL Server 2008 R2
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    <p>I'm hoping you can point me in the right direction.</p> <p>I'm trying to generate a control chart (<a href="http://en.wikipedia.org/wiki/Control_chart" rel="nofollow">http://en.wikipedia.org/wiki/Control_chart</a>) using SQL Server 2008. Creating a basic control chart is easy enough. I'd just calculate the mean and standard deviations and then plot them.</p> <p>The complex bit (for me at least) is that I would like the chart to reset the mean and the control limits when a step change is identified.</p> <p>Currently I'm only interested in a really simple method of identifying a step change, 5 points appearing consecutively above or below the mean. There are more complex ways of identifying them (<a href="http://en.wikipedia.org/wiki/Western_Electric_rules" rel="nofollow">http://en.wikipedia.org/wiki/Western_Electric_rules</a>) but I just want to get this off the ground first.</p> <p>The process I have sort of worked out is:</p> <ol> <li>Aggregate and order by month and year, apply row numbers.</li> <li>Calculate overall mean</li> <li>Identify if each data item is higher, lower or the same as the mean, tag with +1, -1 or 0.</li> <li>Identify when their are 5 consecutive data items which are above or below the mean (currently using a cursor).</li> <li>Recalculate the mean if 5 points are above or 5 points are below the mean.</li> <li>Repeat until end of table.</li> </ol> <p>Is this sort of process possible in SQL server? It feels like I maybe need a recursive UDF but recursion is a bit beyond me!</p> <p>A nudge in the right direction would be much appreciated!</p> <p>Cheers</p>
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