Define the observation
Imagine a shop recording 120 completed purchases from 600 visits during one week. Its recorded purchase rate is 20 percent for that defined set of visits. Before comparing another week, ask whether repeat visits, cancellations and incomplete records were handled in the same way. The arithmetic alone cannot settle the definition.
Compare like with like
Write the numerator and denominator beside every percentage. A count of customers and a count of visits answer different questions, even if they happen to produce the same value. Keep the date range and inclusion rule on the worksheet so another reader can reproduce the calculation.
Leave the conclusion proportional
A changed rate describes the observed records. It does not, by itself, explain why the rate moved or establish that a new policy caused it. Separate the calculation from possible explanations and list the additional observations needed to evaluate each explanation. This example uses invented teaching numbers, not measurements of a real business.
