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Okay, how about this: under what circumstances would my inferring incidence from prevalence in the above question not be legitimate?

Flavorflav wrote:Okay, how about this: under what circumstances would my inferring incidence from prevalence in the above question not be legitimate?

When the duration of the disease is relatively short, for, say, the flu.

Crazy Puny Man wrote:

Flavorflav wrote:Okay, how about this: under what circumstances would my inferring incidence from prevalence in the above question not be legitimate?

When the duration of the disease is relatively short, for, say, the flu.

While that is true, it is not what I was looking for (as I said, "in the above question"). Even for life-long conditions, sometimes you cannot infer age-related incidence from age-specific prevalence. Hint: Polio would be a good example for what I am talking about.

Woops...my bad...

If the case fatality rate is relatively high?

Not your bad - it was a valid answer, just not the one I was looking for. As for your current guess, a high case fatality rate would actually mean that the age effect is even bigger, since the dead youngsters don't show up in the prevalence statistics for older folks. Let me put it this way: how many people do you know with polio?

Flavorflav wrote:Not your bad - it was a valid answer, just not the one I was looking for. As for your current guess, a high case fatality rate would actually mean that the age effect is even bigger, since the dead youngsters don't show up in the prevalence statistics for older folks. Let me put it this way: how many people do you know with polio?

Could the deaths be more spread out, i.e. with more of the older people dying? Or would a high case fatality imply that more young people die than old people?

As for your question...none?

Hmm. I can't think of a disease that you can get diagnosed with when young, has a high case fatality rate, but doesn't kill you until you are older. If there was such a thing then the prevalence among old people would be too low, as the dead are not counted. I'm thinking of something much simpler, though. What would the breakdown of polio look like, stratified by age?

Flavorflav wrote:Hmm. I can't think of a disease that you can get diagnosed with when young, has a high case fatality rate, but doesn't kill you until you are older. If there was such a thing then the prevalence among old people would be too low, as the dead are not counted. I'm thinking of something much simpler, though. What would the breakdown of polio look like, stratified by age?

Do you have to be young when diagnosed? Or is that the most common age at which to be diagnosed?

Crap

Um...younger age groups would have a higher prevalence?

To clarify, I was merely trying to draw out the implications of your guess about case fatality rate.

If polio was common among younger people, wouldn't you know someone who had it?

Flavorflav wrote:To clarify, I was merely trying to draw out the implications of your guess about case fatality rate.

If polio was common among younger people, wouldn't you know someone who had it?

Yes...?

You mean that the prevalence in each age group would be close to zero?