Verifying numbers.
WHY IT REQUIRES SPECIAL CARE
Wrong numbers look plausible, and are acted on.
WHAT TO VERIFY
Calculations against independently computed results Totals against their components Figures against a known reference
WHAT INDEPENDENT COMPUTATION MEANS
Calculating expected results by a different method.
WHY NOT USING THE SAME CODE
It would only confirm the code matches itself.
WHAT TO TEST WITH
Small datasets where the answer can be verified by hand
Edge cases: zero, negative, very large
Empty datasets Data with missing values
WHAT MISSING VALUES CAUSE
Averages computed over fewer items than assumed.
WHAT TO VERIFY ABOUT ROUNDING
That it is applied consistently That totals of rounded values match rounded totals, or that the discrepancy is understood
WHAT TO TEST ABOUT CURRENCY
Conversion, rates applied, and the date used.
WHAT TO TEST ABOUT DATES
Period boundaries Time zones Periods with no data
WHY PERIOD BOUNDARIES MATTER MOST
Off-by-one errors there silently omit or duplicate a day.
WHAT TO RECONCILE
Reports against the source system.
WHAT TO DO ON DISAGREEMENT
Investigate before publishing.
