Outliers explained

An outlier is a point in the last 20% of the historical data that is outside of the confidence range at that point in history.

When forecasting, many models are evaluated to determine which one proves to be most accurate overall, then the one with highest overall accuracy is selected. Although not displayed in Planning Analytics Workspace, the points along the model history have a confidence interval similar to that displayed with the forecasted values. Where many points along the model history may map near exactly to the actual historical points received, there may be a subset that sit outside of the confidence level and it is these points that are highlighted as outliers. This is illustrated here, where you can see a single outlier.

With the confidence bound of the historical data super-imposed onto this chart, we see that, where the value was expected to be ~55k, we have a value of ~20k. The value is outside of the confidence bound, resulting in it being flagged as an outlier.