Run Chart
A Run Chart is a line chart that visually displays data over a period of time. It’s also known as a trend or time series chart.
Why Run Chart?
Run Charts help us to identify patterns that may exist in the data, and trends over time.
When to use Run Chart?
You should use Run Charts whenever you want to understand how your process has performed over a certain period of time or when you want to see if your changes resulted in sustainable improvements.
In a Run Chart we can identify below non-random variations or patterns:
Clusters:
Cluster is one where we can see a group of data points in a particular area in the Run Chart. We can also identify the clustering by looking at the probability value. If the probability value for Clustering is less than 0.05, we will be having clustering of data in the Run Chart.
Mixtures:
If the data points frequently crosses the median line, it’s called Mixtures. We can see than when we pool the data points from more than one population. We can also identify the Mixtures by looking at the probability value. If the probability value for Mixtures is less than 0.05, we will be having Mixture of data in the Run Chart.
Trends:
A trend is defined as a continued drift or float of data. It can be either in the upward direction or downward direction. This is an indication that the process may in near future go unstable. This may cause due to replacement of operators, aspects such as dilapidated tools etc. Trends can be identified by looking at the probability value. If the probability value for Trends is less than 0.05, we will be having Trends in data in the Run Chart.
Oscillations:
When data swings upwards and downwards, it’s called Oscillations. This gives an warning that the underlying process is not stable. Oscillations can be identified by looking at the probability value. If the probability value for Oscillations is less than 0.05, there will be Oscillations in data in the Run Chart.
Comparison of Run Charts Vs. Control Charts:
Below are some comparisons between Run Charts and Control Charts:
Run Chart:
· Run Chart is simple and can be created easily,
· Can be quickly analyzed
· A person looking at a Run Chart does not require statistical knowledge to read the chart
However, a run chart lacks the below advantages which a Control Chart possesses:
Control Charts:
· A control chart will help us understand whether the process is stable or in control
· Is the process in the correct track