Kudos to the author for attacking the question this way, it's always important to look at data and try to model it. (and it's a lot of work!) Unfortunately, I'

Kudos to the author for attacking the question this way, it's always important to look at data and try to model it. (and it's a lot of work!) Unfortunately, I'm pretty sure there's a fatal flaw in the analysis. Suppose we had two types of years, both following a Poisson Distributino, but one with a higher incidence, the other with a lower incidence, and they alternated[1]. Now sample each type of year separately. Each will give you a Poisson distribution. To get the distribution of all years you'd just add bins of the two types together. The sum of two poisson distributions is a poisson distribution (with a different mean), therefore, we cannot conclude anything about how the mean value is changing with time (and thus, answering the question: is the incidence rate rising) unless we actually bin the data by year, and see if the mean value is changing with time. Unfortunately, by splitting time up, we reduce the already small sample sizes for each bracket. Time series analysis is a more appropriate tool to tackle this question. [1] This is unchanged if the rate is continuously increasing, the setup was so that you can actually think of collecting the same data over multiple years.