The box-and-whisker plots are very effective and easy to read. They summarize data much better than just a simple ‘average’, and provide a deeper insight into the distributional characteristics of a group of scores. Here’s how they work:
To begin with, scores are sorted. Then four equal sized groups are made from the ordered scores, That is, 25% of all scores are placed in each group. The lines dividing the groups are called quartiles. The ‘inter-quartile range, aka the ‘middle box’, represents the middle 50% of scores for the group. Now for the whiskers- the upper and lower whiskers represent scores outside the middle 50%. Whiskers often (but not always) stretch over a wider range of scores than the middle quartile groups do.