A histogram is a graph that displays the shape of the distribution of numerical data. A histogram can have many different shapes. The three common shapes are symmetric, skewed right, and skewed left.

A symmetrical distribution

The above histogram has one mode (unimodal), and it is symmetrical, in other words, if you fold the histogram in half, one part can take the place of the other part. In a perfectly symmetrical distribution, the mean, the median, and the mode are the same.

The two histograms below are not symmetrical. The data distributions are skewed.

A negatively skewed distribution

If the data distribution is negatively skewed, it is skewed to the left, that is the long tail is on the left side, the mean is less than the median, and the median is less than the mode.

A positively skewed distribution

If the distribution of data is positively skewed, it is skewed to the right, that is the long tail is on the right side, the mode is less than the median, and the median is less than the mean.