Unusual values.
WHAT AN OUTLIER IS
A value far from the rest.
WHAT IT MIGHT BE
An error A genuine exception The most important record you have
WHAT NOT TO DO
Remove it automatically.
WHAT TO DO
Investigate it.
WHAT INVESTIGATION REVEALS
An entry error, which should be corrected A one-off event, which should be noted A genuine pattern beginning
WHAT OUTLIERS DO TO ANALYSIS
Pull averages Distort charts Dominate totals
WHAT TO DO WHEN ONE DISTORTS A FINDING
Report with and without it, and explain.
WHAT NEVER TO DO
Remove it silently.
WHAT TO RECORD
That it existed and what you concluded.
WHEN TO EXCLUDE
When it is genuinely an error, or genuinely unrepresentative and you say so.
WHAT TO LOOK FOR
Outliers appearing repeatedly, which is a pattern rather than an exception.
WHAT THAT INDICATES
A segment you have not identified.
