Averages are misleading when used to compare different groups, apply group behavior to an individual scenario, or when there are numerous outliers in the data. The root causes of these problems appear to be over-simplification and rationalizations — what people want to believe.

Why is average not a good measure?

The mean is not a good measurement of central tendency because it takes into account every data point. If you have outliers like in a skewed distribution, then those outliers affect the mean one single outlier can drag the mean down or up. This is why the mean isn't a good measure of central tendency.

What is wrong with using averages?

And that is the basic problem with averages: they can hide what you need to know. Averages hide variation. Averages are simple to calculate and are sometimes a lazy way of determining past performance. For example, over some period of time a performance level may have started at 50% and ended up at 70%.