Statistical Process Control (SPC) charts

Statistical Process Control (SPC) charts are now available on the Model Health System. Just go to the top right of your interactive chart and select from the drop-down menu.

SPC is an analytical technique that plots data over time. It helps people understand variation and can guide them to take the most appropriate action.

  • SPC alerts us to a situation that may be deteriorating
  • SPC shows us if a situation is improving
  • SPC shows us how capable a system is of delivering a standard or target
  • SPC shows us if a process that we depend on is reliable and in control

An SPC chart is a time series line chart with three reference lines that help you appreciate variation in the data. In the Model Health System, the reference lines are:

  • centre reference line: the mean
  • upper and lower reference lines: the process limits, also known as control limits.

The limits are defined by the variability of data for the measure plotted on the chart.

SPC rules

A set of rules allows you to interpret SPC charts and help you understand when something unusual is happening. There are four SPC rules in MHS:

  •  A single point outside the control limits
  •  Two out of three points are within one sigma of a control limit
  •  Seven or more consecutive points above or below the mean line
  • Seven or more consecutive points increasing or decreasing

Where a data point breaks one or more of these rules it is plotted in colour on the SPC chart. 

Improvement is shown by a blue dot, deterioration is shown by an orange dot.

Regular training sessions are run by the Making Data Count team. If you're interested, find out more here: :

To access the Making Data Count training dates you will need to sign up to the futures site first:

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