Skewedness

Symmetric
A distribution is said to be symmetric when the observations are arranged in a similar way on both sides of the median - as in the histogram below.


In roughly symmetric distributions the mean is roughly equal to the median.

Right Skewed
A distribution is said to be right skewed when most of the observations are clustered around the median while a few observations have significantly higher values - as in the histogram below.


In right skewed distributions the mean is greater than the median.

Left Skewed
A distribution is said to be left skewed when most of the observations are clustered around the median while a few observations have significantly lower values - as in the histogram below.


In left skewed distributions the mean is less than the median.