Step I rare disease assumption

[Mleechu]

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Hey. I am having a hard time understanding the concept behind rare disease assumption . I know that is says when dz prevalence is low we can say odds ratio = Relative risk but i don't exactly know what's going on.

 

[worldbeater]

I don't know what rare disease assumption is, but odds ratio always refers to retrospective studies while relative risk refers to prospective studies.

 

[Mleechu]

I don't know what rare disease assumption is, but odds ratio always refers to retrospective studies while relative risk refers to prospective studies.

Yep. That I know. But FA says if disease prevalence is low we can say OR = RR. I know this is known as "Rare Disease Assumption". But I am having trouble understanding why low prevalence would cause OR to become equal to RR.

 

[mcloaf]

This page has a nice explanation of the math. http://books.google.com/books?id=sO...ow prevalence rare disease assumption&f=false