Thursday, June 02, 2005

Good control chart - shame about the trend line!


Posted by Hello

I found this old chart today. It’s a monthly chart of percentage of incidents where a police force has responded to a 999 call within the target time allowed.

The run line tells a story in itself, but the chart is possibly more interesting for its misuse. Note how the person who constructed it has put in upper and lower control limits, but replaced the average line with a line of best fit trend!

Oh dear, oh dear……..

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