I have been puzzling about incidence rates, prevalence and recovery rates for some years now. Am I correct in assuming an incidence rate reflects the probability that someone will fall ill with the condition during that year, that prevalence indicates the number or proportion of people with the illness in the community, and that recovery rates reflect the probability that someone will recover from the condition during that year? If so I started to produce a spreadsheet looking at numbers in the UK. It is a very primitive one, but one I can modify to reflect reality a little more closely. But I am not confident of my mathematical analysis these days, so have attached it. I assumed a population of 64 million in the UK, a life expectancy of 80, no difference between males and females, no death rates, a uniform spread of people in each age group, and no recovery. I know these are daft simplifications, but it gets the layout going. The problem is that to reach a total of 250,000 people with ME in the UK, and assuming that anyone from 12 to 75 can be diagnosed with ME, I need a prevalence rate of 0.6%. A uniform prevalence rate is reasonable (I know people suggest there are peaks, but the PACE trial had a pretty uniform age distribution). Before I start to tweak things, am I on the right tracks?