We often display percentages which sum is expected to equal 100%. For example, in a pie chart. These percentages are sometimes rounded, either for clarity (25% instead of 25.434%) or because we have to (67% instead of 66.66666...%).
However, this can lead to inconsistencies. For example, take a 1/3-1/3-1/3 situation. We have three percentages, all equal to 33.333333...%. These percentages have to be rounded, whatever it is 33.33% or simply 33%. But 33% + 33% + 33% is equal to 99%, not the expected 100%.
I see two solutions:
- Just use 33%. It is up to the user to realize that the mistake is due to rounding issues.
- Adjust one of the percentage: 33%, 33% and 34%. The sum is equal to 100%, which is satisfying. However, the percentages are not identical, which is somehow misleading.
What are the best practices?