A common mistake is to confuse the average percentage with the percentage of averages. The average percentage is the mean of the percentages, while the percentage of averages involves averaging the base values first and then calculating the percentage.
For example, if you have two classes: Class A (20 out of 40 students passed = 50%) and Class B (30 out of 60 students passed = 50%), the average percentage is 50%. But if you combine the data: (20+30)/(40+60) = 50/100 = 50%. In this case, both are the same, but if the percentages are based on different totals, the results can differ.
Always ensure you are using the correct method for your data. If the base values (denominators) are different, the average percentage may not reflect the true overall percentage.
Double-check your calculations and understand the context of your data before interpreting the results.