Run charts give a picture of a variation in some process over time and help detect special (external) causes of that variation. They make trends or other non-random variation in the process easier to see and understand. With the understanding of patterns and trends of the past, groups can then use run charts to help predict future performance.

When to Use a Run Chart

If data analysis focuses on statistics that give only the big picture (such as average, range, and variation), trends over time can often be lost. Changes could be hidden from view and problems left unresolved. Run charts graphically display shifts, trends, cycles, or other non-random patterns over time. They can be used to identify problems (by showing a trend away from the desired results) and to monitor progress when solutions are carried out.

How to Use a Run Chart

A run is the consecutive points running either above or below the center line (mean or median). The points in a run chart mark the single events (how much occurred at a certain point in time). A run is broken once it crosses the center line. Values on the center line are ignored: they do not break the run, nor are they counted as points in the run. The basic steps in creating a run chart follow.

Run Chart of Arterial Hypertension Patients under Observation (per 1,000) in Tula Oblast, Russia

Step 1. Collect at least 25 data points (number, time, cost), recording when each measurement was taken. Arrange the data in chronological order.

Step 2. Determine the scale for the vertical axis as 1.5 times the range. Label the axis with the scale and unit of measure.

Step 3. Draw the horizontal axis and mark the measure of time (minute, hour, day, shift, week, month, year, etc.) and label the axis.



Step 4. Plot the points and connect them with a straight line between each point. Draw the center line (the average of all the data points).

The following provide some guidance in interpreting a run chart:

• • Eight consecutive points above (or below) the center line (mean or median) suggest a shift in the process
• • Six successive increasing (or decreasing) points suggest a trend
• • Fourteen successive points alternating up and down suggest a cyclical process

Caution

Be careful not to use too many notations on a run chart. Keep it as simple as possible and include only the information necessary to interpret the chart.

Do not draw conclusions that are not justified by the data. Certain trends and interpretations may require more statistical testing to determine if they are significant.

Whenever possible, use a run chart to show the variation in the process. Do not assume that the variation is so clear and obvious that a run chart is unnecessary.

A run chart must not lie or mislead! To ensure that this does not happen, follow these guidelines:

• • Scales must be in regular intervals
• • Charts that are to be compared must also use the same scale and symbols
• • Charts should be easy to read