Calculate the mean: 21 points / 25 regions =
0.84
Graphical evidence:
H_{0}: The observed frequencies
agree with the expected frequencies
H_{1}: The observed frequencies do
not agree with the expected frequencies
Test statistic: (using Excel)
Observed 
Expected 
(Observed  Expected)^2/Expected 
11 
10.79276309 
0.003979253 
9 
9.065920992 
0.000479331 
3 
3.807686817 
0.171326589 
2 
1.066152309 
0.817961471 





0.993746644 
Note: the Expected values are calculated using
=25*POISSON(ROW()2,0.84,FALSE)
pvalue: =CHIDIST(0.9937,3) = 0.8028
Conclusion: Since 0.8028 > 0.05, fail to reject the null
hypothesis. The observed values follow a Poisson distribution.
Note: The animation on the Overview page
should have the Poisson distribution skewed more to the right.
Apparently, the author chose a different model for aesthetic
reasons.