# Distribution of the square of a non-standard normal random variable

What is the distribution of the square of a non-standard normal random variable (i.e., the mean is not equal to 0 and the variance is not equal to 1)?

## 1 Answer

It is a scaled non-central chi-square distribution with one degree of freedom. More specifically, if $Z$ is a normal random variable with mean $\mu$ and variance $\sigma^2$, then $\frac{Z^2}{\sigma^2}$ is a non-central chi-square random variable with one degree of freedom and non-centrality parameter $\lambda=\left(\frac{\mu}{\sigma}\right)^2$.

• The non-centrality parameter in the non-central chi square is the square of the mean of the normal distribution in question. What is the scaling factor that we multiply the non-central chi square by to account for the variance of the normal distribution not being equal to 1? Mar 13 '16 at 19:44
• Just made an edit to address this. Mar 13 '16 at 20:12
• To make it even more concrete for those of us who like concrete, to generate m random values of Z squared, in R you can use Z2 <- s^2 * rchisq(m,df=1,ncp=(mu/s)^2) Mar 14 '16 at 9:31