Qlikview Lean tips #1: How to highlight series of points that violate control rules on a chart

Highlighting patterns of points on a chart






Control charts are charts that plot some sort of quality measurement, for example number of defective goods in a batch or the weight of packets of food. The measurements are then plotted over time to see if there are any patterns. I won't go into too much more detail, because this is not the place for it (and I don't want to bore anyone that already knows it!).

You then draw "control limits" - lines above and below the average and then investigate any points that fall outside those lines, or meet some criteria. What those criteria are, and where to set the control lines are dependant on the quality control system you have in place, and the type of data etc. Lean Six-Sigma is perhaps the most famous set of rules for determining when to take action.

In general the rules are often things like:

• X number of points above the average line
• X number of points increasing each time.

It's fairly easy to create a control chart with the limits, but a bit more complicated (judging from questions I get asked) to highlight every single point in a "run" that has violated the pattern, especially dynamically (as in not in the script). It's easier to just mark 1 (the start or end).
 
So how do you highlight "X points in a row"?

Welcome

Hi there!


I work as a QlikView developer in the NHS, (UK National Health Service), designing dashboards for NHS organisations across Britain. Along the way, I've picked up a few tips which I'd like to share with you here on this blog.

This blog isn't just for QlikViewers working in health care organisations. It's for anyone that comes across similar problems and analyses that we do. So this could be things like working with very large, complex datasets or needing the bend the rules of what QlikView can do. And particularly being able to create statistical charts.

I hope to cover topics like incorporating SPC / 6 sigma charts, matching intervals to track patient journeys and anything else that I find interesting or have been involved in!

And please feel free to leave any comments, ideas or if you would like me to explain anything a bit more.


Erica :)