2.2.3 - Shape

Quantitative variables are often discussed in terms of their shape. Both dotplots and histograms can be used to interpret a distribution's shape. A distribution may be described in terms of symmetry and skewness.

Symmetrical Distribution

A distribution that is similar on both sides of the center.

Symmetrical Distribution 6 0 2 4 6 8 10 12 8 10 12 14 X Frequency
Normal Distribution

One specific type of symmetrical distribution. This is also known as a bell-shaped distribution. 

Distribution Plot Normal, Mean=0, StDev=1 -3 0 0.1 0.2 0.3 0.4 -2 0 -1 1 2 3 X Density
Skewed
A distribution in which values are more spread out on one side of the center than on the other.
Right Skewed

A distribution in which the higher values (towards the right on a number line) are more spread out than the lower values. This is also known as positively skewed.

Right Skewed Distribution 6 4 2 0 0 2 4 6 8 10 12 14 16 18 8 10 12 X Frequency
Left Skewed

A distribution in which the lower values (towards the left on a number line) are more spread out than the higher values. This is also known as negatively skewed.

Left Skewed Distribution 6 4 0 5 10 15 20 8 10 12 X Frequency