5.1. The Standard Normal Probability Distribution http://www.ck12.org
Assessing Normality
The best way to determine if a data set approximates a normal distribution is to look at a visual representation.
Histograms and box plots can be useful indicators of normality, but are not always definitive. It is often easier to tell
if a data set isnotnormal from these plots.
If a data set isskewed rightit means that the right tail is significantly larger than the left. Likewise,skewed left
means the left tail has more weight than the right. Abimodal distributionhas two modes, or peaks, as if two normal
distributions were added together. Multimodal distributions with two or more modes often reflect two different types.
For instance, a histogram of the heights of American 30-year-old adults, you will see a bimodal distribution – one
mode for males, one mode for females.