A trend of 7 or more consecutively plotted points in either an upward or downward direction indicates the potential presence of a special cause in the process.
|UCL = Upper Control Limit|
|LCL = Lower Control Limit|
|= Mean (average of all the values (subgroup averages))|
Note: 2 consecutive plots of the same value are considered part of the same trend.
Trends can indicate process change resulting from many things, for example:
A downward trend indicates an improvement on Range, Standard Deviation, and Attribute charts.