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.
This exercise is part of the course
Generalized Linear Models in Python
Exercise instructions
- Use
numpy
mean()
to compute and print sample mean for number of satellites variablesat
assat_mean
. - Use
numpy
var()
to compute and print sample variance for number of satellites variablesat
assat_var
. - Compute and print ratio of
sat_var
tosat_mean
.
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
# Compute and print sample mean of the number of satellites: sat_mean
____ = np.____(____.____)
print('Sample mean:', round(____, 3))
# Compute and print sample variance of the number of satellites: sat_var
____ = np.____(____.____)
print('Sample variance:', round(____, 3))
# Compute ratio of variance to mean
print('Ratio:', round(____/____, 3))