Exercise

# Is the mean equal to the variance?

Under the Poisson model one of the assumptions was that the mean should be the same as the variance. As you learned in the lecture, if this assumption is violated then there is **overdispersion**. Without adjusting for overdispersion you would wrongly interpret standard errors of the given model.

In this exercise you will first compute the mean and the variance of the number of satellites for the female crabs.

The `crab`

dataset is loaded in your workspace.

Instructions

**100 XP**

- Use
`numpy`

`mean()`

to compute and print sample mean for number of satellites variable`sat`

as`sat_mean`

. - Use
`numpy`

`var()`

to compute and print sample variance for number of satellites variable`sat`

as`sat_var`

. - Compute and print ratio of
`sat_var`

to`sat_mean`

.