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I’ve been thinking about doing a control chart post for a while now. Control charts go back to the 1920’s and one normally encounters them in the context of W. Edwards Deming, though they were actually originated by Walter A. Shewhart, and Quality Assurance. They are used to examine variation in the output of processes, principally with the aim of determining whether the process is in a state of “statistical control”.

In a process that is in statistical control, the causes of variation are in the system all the time and one may predict, within statistical bounds, the future performance of the system. A typical example from Deming might be normal variation in raw materials from a supplier, though it could equally apply to the difficulty of helpdesk calls entering a service desk.

For a system that is not in statistical control variation is introduced from causes that are external to the system and are not present at all times. A Deming example would perhaps be a change in the supplier of raw materials. An IT example might be a major system change resulting in a sudden increase in calls of a certain type. Clearly this undermines ones ability to reliably predict future process performance.

I thought it might be nice to see if my LinkedIn presence was in statistical control.  That way, if I now make some changes to my profile, it should be possible to determine whether the effect is significant, or lost in the statistical noise of LinkedIn. This is possible because if the process is in statistical control, we can use the past behavior to come up with an expectation of what the system would produce in the future, in the absence of external sources of variation

The LinkedIn “Who’s Viewed Your Profile” graph gives weekly profile views going back 90 days. To begin with, let’s look at the relatively small number of views that I’ve been getting:

To turn this into a control chart, we calculate the mean (2.6) and the standard deviation (1.4). We now plot two lines at mean +/- three standard deviations:

So, two things are clear.

1. The process is in statistical control. Based on the past 90 days, we can expect to see profile views between 0 and 7 with a mean of 2.6.
2. The process is not very tightly bounded.
3. I could use more traffic to my profile.

In my next post I’m going to update my profile with some of the various things LinkedIn suggest, and see what happens.