Our dataset said the average loan was 2.3 million kroner. The number that actually mattered was 255,000. Both were correct. Only one of them was true.
This is a writeup of three ways a dashboard can be arithmetically perfect and still lie, using real figures from an analysis of 1,000 Norwegian debt consolidation applications. If you build reporting for anyone, you have probably shipped at least one of these.
1. Summing a field that contains two different things
A debt consolidation loan pays off your expensive credit card debt. It also, if you own property, rolls your existing mortgage into the same new loan. Same column in the database. Same loan_amount. Utterly different meaning.
SELECT AVG(loan_amount) FROM applications;
