What is the difference between Run Chart and Control Chart ?

 

Control charts and run charts are essential tools in quality management that help you identify trends or errors in the product or the process. These charts let you know:

  • How the process is performing.
  • Today’s vs. yesterday’s performance.
  • Whether you are performing as planned.

 

Run Chart:

 

A Run chart is a line chart of data plotted overtime. The continual plotting of data enables you to uncover trends (upward and downward) and patterns in your project/process. This chart offers straight forward visualisation of data, making this chart type easy to analyse. There are limitations as they do not display statistical control limits, so don’t detect unusual levels of variation with the same fidelity as a Control chart can. However this chart still has the ability to identify Common Cause and Special Cause Variation.

    • Through analysis of a run chart, the following can be derived:
      • changes / trends of the process over time
      • any pattern / cycle of the process
    • Examples of a run chart:
      • progress of the project / processes / tasks (percentage completion over time)
      • expenditure of the project
    • Plus: A run chart is easy to draw and interpret. It is useful for analysis of simple processes.
    • Minus: Cannot show if the process is in control or stable. Not quite useful for quality control.

Run Chart PMP

Run Chart Example

Download Free Run Chart Template

Control Chart:

 

A Control chart is a more advanced version of a Run chart. You may hear this chart referred to as a Shewhart chart. Whilst this chart still plots a single line of data, it also displays an upper line for the upper control limit and a lower line for the lower control limit. These lines allow you to identify the difference between normal and unusual variation in data and also whether the variation is positive or negative.

A Control Chart also plots the data of a variable over time (same as the run chart), but also includes specification limits (Upper Specification Limit USL and Lower Specification Limit LSL) and control limits (Upper Control Limit UCL and Lower Control Limit LCL).

    • Specification Limits: provided in the project plan / contract as a project requirement of the process;
    • Control Limits: specified by the quality requirements of the process (e.g. 3-sigma); if a data go beyond the control limits or a pattern/trend has been formed, corrective actions must be taken to correction the deviation.
    • Tells whether the process is under control
      • Telltales of “Out of Control”:
        • Any data point outside the control limits
        • Rule of 7: 7 consecutive data points within the control limits but on either side of the mean
        • A trend has been formed (e.g. 6 consecutive points forming an increasing or decreasing trend)

To put it another way, a Control Chart is a Run Chart with 4 line indicating the limits added (upper/lower specification limits and upper/lower control limits) (plus optional a line indicating the mean of all data).

Control Chart PMP

Control Chart Example

Download Free Control Chart Template