Doubt regarding Incidence and Prevalence (Denominator of equation)

[voicesinmyhead]

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First Aid 2015 pg.49 tells us that both prevalence and incidence rate have the denominator of number of people at risk.

I'm wondering if this is wrong for prevalence. Won't prevalence have the denominator of total population instead?
[http://www.cdc.gov/ophss/csels/dsepd/ss1978/lesson3/section2.html]


It has been submitted by some users for first Aid errata, but rejected by the editors repeatedly.

Confused.

 

[Transposony]

Denominator has to be population "at risk" to be a case.
For example, if you are looking at prevalence of ovarian cancer, then, it has to be women of certain age group (at risk) not other people i.e. men etc who can be the denominator.

 

[voicesinmyhead]

@Transposony

Thanks! Does this mean the denominator for prevalence would still include people who currently have the disease? (the ones we usually exclude during incidence calculation)

 

[Transposony]

Thanks! Does this mean the denominator for prevalence would still include people who currently have the disease? (the ones we usually exclude during incidence calculation)

No, since the people who currently have the disease are the "Numerator".
The main difference between Incidence and Prevalence is that "New cases" and "All cases" respectively.