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Applying Statistical Process Control to Health Monitoring

Statistical Process Control (SPC) is the widely recognised method for analysing and monitoring process capability. It is entrenched in the continuous improvement methodology of Six Sigma and other Quality Management philosophies, and provides a pratical, visual approach for evaluating both input and output CTQ (Critical to Quality) indicators. Whilst Six Sigma employs a number of statistical methods (such as Control Charts and Pareto analysis) to improve production efficiencies and achieve process stability, SPC can employ any number of analytical and graphical techniques to achieve quality objectives.

Whilst Pareto Charts are reasonably straight forward to understand and apply (see our Pareto Analysis article and Smart Guide), many people and managers struggle to fully comprehend and apply SPC and Process Control Charts.  There are many excellent books and online training on the topic, so I don't intend to make this a training document. I particulary recommend the publication for ASQ - SPC for Right Brain Thinkers (Lon Roberts).

To help visualise the use of SPC, I'd like to provide a simple application to monitoring health stability for Type 2 Diabetics (also known as NIDD or NIDDM).  It can also be applied to the unprecedented number of people in the high risk area of acquiring NIDDS.  Note that the model discussed here is not intended to replace any professionally prescribed health plan.  Many people however with NIDD or at risk of acquiring it, are left without any form of plan to improve the quality of their health, and minimise the effects of the disease, or the risks of contracting diabetes.


This article and demonstration is targerted at people with a basic understanding of Microsoft Excel.  I've also provided the Health Tracker tool for download by all who wish to try it for themselves (or support someone close to them).  Being type 2 diabetic myself, I have been using the tool for a while now to help manage my own situation. The graphical reports are generated automatically and the tool has given me a greater sense of control.  You can download the Health Tracker tool from our Smart Guides index.

 

 

To start with, I researched and played with a number of freely available Control Chart tools, and settled on the Microsoft Office Control Chart template (for MS Excel). The thing I liked about this template was that the macros (formula) were exposed in the data worksheet.  I could see how the the mean and standard deviations were calculated as well as the upper and lower control limits.  The LCL and UCL could easily be modified from 1s to 2s and so forth.  Of course the columns containing the macros could easily be hidden, although this would require a minor change to the chart attributes (I'll create an alternative version if enough interest is fed back to me).

This template, as in the Health Tracker model, can be extensively modified to track parrallel data pertinent to individual needs and tool application. In my case I considered that the CTQ inputs and symptoms were:

  1. Blood Glocose levels
  2. Weight
  3. Blood Pressure
  4. Diet
  5. Exercise
  6. Medication
  7. Sleep

I charted the daily progression of the the 1st three health factors, whilst the last four factors were tracked qualitatively, yet essentially for understanding variation in blood sugar levels.


There are only 2 worksheets in the tool, the data tab and the report tab.  The data and reports are maintained for a month at a time and closed off. Only the start date needs to be entered and the yellow coloured columns contain formulas that should not be overwritten. At the start of each month, start off on a new copy of the template, and spend some time with family to discuss the effects of lifestyle and diet on montly trends. Just as importantly,  make a determined plan to modify lifestyle regimens to improve the process and outcomes.

The whole idea is to track at least one sugar reading per day (eg. the post overnight reading before breakfast), along with weight and blood pressure readings. Additional information affecting health (such as diet, medication, execise and sleep) should be relevant and honest. If one was taking the same medication every day, exactly as prescribe - then there would be no need to track that.  In the above example, The dosage was varied for one medication that would sometimes adversely lower overnight sugar levels.  One could take the monthy report and discuss this with the medical physician.

The following standard reports were generated, but other custom charts could be added or modified to suit.

 

 

Whilst there are many of very clever Quality Analysts (and Six Sigma gurus) in the world who live and breathe SPC, the topic is often beyond the reach of the masses who could benefit from this breakthrough methodology, perhaps in life changing ways. Feel free to provide feedback on both the tool, any personal benefits and the underlying methodology.


 

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Comments

Hiding the Control Chart formulas (in columns G through M) is easy, but the data is ignored in the chart (Report tab) by default.  You can rely on TechRepublic.com to explain the solution in plain english, for multiple versions of Excel.

Here are the steps in MS Excel 2007 -

  1. Select the chart.
  2. Click the Design tab.
  3. Click Select Data in the Data group.
  4. Click the Hidden And Empty Cells button (at the bottom).
  5. Select the Show Data In Hidden Rows And Columns option.
  6. Click OK twice.

We'll fix this in Version 4 of the Health Tracker tool.

For those people who have found the Tracker useful, but would prefer not to see the formulae (or are not particularly interested in Six Sigma), I made the simple changes to the template. You can grab it here.

Health Tracker Template V04

Further discussions on this topic and development of the HealthTracker tool may be followed through my blog. Whilst commenting on blogs is only available to logged in users and QualityHelp Community members, feel free to post suggestions and feedback through the webform attached to this article. We are very keen to get both.

We've already released the next version of the tool ahead of schedule.

There are now two versions (5a and 5b) of the Healthtracker template, to hopefully cover International and USA units for blood glucose levels. Version 5a of the Healthtracker uses the international units  (mmols/L), wilst the new Version 5b uses mg/dL. The latest versions can also be downloaded from our Smartguides section.

Note also that we have made the date formats generic. We hope to merge the two templates for Version 6.

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