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Friday, September 7, 2012

EV Based Trend Display - Trubin's Criterion!

Very typical task is to display trend direction on a dashboard type of report. Here is an example from SAS website:


















But how correctly to choose the direction? Based on what? My suggestion is to use Exception Value (EV) meta metric (Check how that should be calculated here: EV-Control Chart). Indeed, for the given most recent time period (e.g. day, week or month) EV will be greater than 0 , if more UCL crossings happened than LCL crossings; EV  will be 0 if everything occurred within UCL-LCL band; and EV will be less than 0, if more LCL crossings happened than UCL crossings. 

That criterion have been already used to detect most recent trends, but the same way that could be used to choose the right direction for the trend arrow on dashboards!

So the Trubin's Criterion would be: