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Control Chart

Control Chart

What is Control Chart?

The control chart is a statistical analysis used to study how a process changes over time. Data are plotted in time order. Control charts are used to routinely monitor quality or simply you can say, control chart is process improvement technique.

What is a process?

A process is simply what we do. It can be filling out an expense report, checking a person into a hospital, burning a CD with music, driving to work, filling a prescription, etc. All these process generates the data. We take these generated data and plot on control chart to improve efficiency.


There are many types of control chart, but we are going to use the basic control chart with Std dev method to understand the concept.


Followings are some scenario where we can use the control chart

1) In manufacturing to test if machinery are producing products within specifications.

2) suppose you want to reduce the time it takes to admit someone to the hospital.

3) If you want to know how views are going up or down for particular website.


Components of Control Chat

1) Avg line

2) UCL (Upper Control line) = Avg Value + Std Deviation* Std Dev Multiplier

3) LCL (Lower control line) = Avg Value - Std Deviation* Std Dev Multiplier


So, basically we can see which are the points "Out of Control" or "In Control".


You can control your Std Dev multiplier using variable.


How to create the Control Chart.


1) Create the Combo Chart.

2) Take any Time dimension of your interest which is suited for your analysis, here I have taken the MonthYear. Also    make it Continuous in Axis setting

3) Create two Expression, one for Line and second for Symbol.


4) Create expressions for Avg line, UCL & LCL which will be used as reference lines in the chart. Check the Chart properties ->Presentation for reference line setting.




5) Create the Background color setting for Symbol expression


if( sum(Sales) < vUCL and sum(Sales) > vLCL, LightGreen(), LightRed())

6) Finally the chart will look like below


There are some other useful links available to create the control charts

QlikView Control (SPC) Chart

See also :

Benford's law

Bollinger Bands

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Comments
aniketsr
New Contributor III

Good one Kushal.

manojkulkarni
Valued Contributor II

Good information. Thanks for sharing

TFS Kushal

ecolomer
Honored Contributor II

Good work,

Thank's for sharing

Saludos,

Enrique Colomer

johnmackintosh
New Contributor III

Be sure to use the correct calculation for standard deviation.

It won't be correct if you use the 'regular 'standard deviation (also applies to Excel etc).

ahaahaaha
Honored Contributor

Thank you for the interesting information.

Not applicable

good work Mr. Kushal.

really nice.

Thanks for such info.

Not applicable

Good Work Kushal.

Keep sharing such great stuff

terrusie
New Contributor II

Hello Kushal,

I've noticed that the scope of the color expression, unfortunately, does not match the dimension of the chart.  For example, what if the dimension was a grouping of work orders,  the expression was the sum of all hours logged to that work order, and the work orders were sorted by latest timestamp in each work order.  When you go to set the color expression, the scope of the color is not specific to the work order.


To make this analogous to your example, imagine if your Sales data were individual sales timestamped at the date of transaction, rather than grouped by month, and your dimension was something like month(date).  When you went to get the color, this dimensional scope would be lost, and sum(Sales) would return the sum of all sales rather than just those for that month.

My assumption is that your individual Sales data are already grouped by month.

Is there a workaround for this?

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‎03-20-2016 03:37 AM
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