Why this matters
Every report you write as an analyst or M&E officer will contain averages, percentages and comparisons. If you misread them, you can send a manager or donor in the wrong direction. A few simple ideas protect you from the most common mistakes.
Mean and median
The mean is what most people call the average: add all the values and divide by how many there are. The median is the middle value when you sort them.
Imagine five traders in Tamale Central Market report their daily sales in cedis: 80, 90, 100, 110 and 900. The mean is 1,280 divided by 5, which is 256. The median is 100. One trader with a very big day pulls the mean far above what a typical trader earns. When a few values are extreme, the median usually describes the typical case better. Good analysts report both and say which one they used.
Percentages and percentage points
A percentage compares a part to a whole. If 45 of 60 pupils attended school on Monday, attendance was 45 divided by 60, which is 75 percent.
Be careful with changes. If attendance rises from 60 percent to 75 percent, it went up by 15 percentage points. In relative terms that is a 25 percent increase, because 15 is a quarter of 60. Both are correct, but they sound very different, so always say which one you mean.
Spread
Two groups can share the same average and still be very different. Spread tells you how far values sit from the middle. The simplest measure is the : the largest value minus the smallest. A standard deviation is a more careful measure of spread that you will meet in spreadsheet functions. For now, remember that an average without any sense of spread hides a lot.