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# Re: st: higher occurrence of disease X in rare disease Y

 From Doug Hemken To statalist@hsphsun2.harvard.edu Subject Re: st: higher occurrence of disease X in rare disease Y Date Thu, 05 Dec 2013 08:20:54 -0600

```If your sample size is literally six cases, then your unconditional probability of seeing disease X is 0.145. If there is no relation between Y and X, it wouldn't be too unusual to see 1 case of X crop up in 6 cases of Y. This is from a binomial distribution.

On 12/05/13, "tiong21@netzero.net"  wrote:
> The prevalence of disease (X) is 1 in 36 in the general population. In a sample population with a very rare disease (Y) of unknown etiology, the prevalence of disease X is 1 in 6 ( ie: 1 case of X was found in the sample population of 6 rare cases of disease Y. How do I show statistically that this higher occurrence of disease X in rare disease Y is not due to chance? And as a corollary suggest that disease X may be a contributory factor in the etiology of disease Y (an issue of causality). Furthermore, should a Poisson distribution be used to calculate the probabilities? A sample Stata script will be much appreciated.
>
>
> Tiong The
> tiong21@netzero.net
>
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--
Doug Hemken
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```