Statistics
Skewness
A measure of the asymmetry of a distribution around its mean.
What is Skewness?
Skewness quantifies how much a distribution leans to one side. A right-skewed distribution has a long tail extending toward higher values, while a left-skewed distribution has a long tail toward lower values.
Why Skewness Matters
High skewness pulls the mean away from the median and violates assumptions of normality. Researchers must identify skewness to decide if data transformations or non-parametric tests are necessary.
Example
Household income data is typically heavily right-skewed, as there is a hard floor at zero but a very long tail of high-income earners.
Common Mistakes
- Confusing the direction of the skew: right-skewed means the tail is on the right, not that the bulk of the data is on the right.
- Applying log transformations to skewed data that contains negative numbers or zeros without properly adjusting the values first.