Flag Outliers in Power Query M

Flags rows whose numeric value falls outside a set number of standard deviations from the column's average.

Conditional LogicAdvancedoutliersstandard deviationflagstatistics

Power Query M code

let
    Source = YourTable,
    Average = List.Average(Source[Value]),
    StdDev = List.StandardDeviation(Source[Value]),
    AddedIsOutlier = Table.AddColumn(Source, "IsOutlier", each Number.Abs([Value] - Average) > (2 * StdDev), type logical)
in
    AddedIsOutlier

Notes

2 standard deviations is a common default; tighten or loosen the threshold depending on how sensitive the flag should be.

Requirements

How to use this snippet

  1. In Power BI Desktop, choose Transform data to open Power Query, then open the Advanced Editor on a query (or start from a blank query).
  2. Paste the snippet and replace the placeholder names (tables, columns, file paths) with your own. Check the requirements above first.
  3. Run it through the Power Query M Formatter to tidy the layout.

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