This is based on a poll somewhere else on this site. I've replied to that post but figured I would start it's own thread as well.

Now, looking at this poll you may not conclude that there is any correlation, but I've included the worldwide percentages and taken into account that even though the highest two blood types are A+ and O+, this doesn't mean someone who is either A+ or O+ is more likely to have

Crohn's, but rather it is more likely in general to be A+ or O+.

So lets the numbers into perspective. AB- is actually only found is roughly 0.5% of the population. Given that 158 people have filled out the poll, 0.5% of 158 is .79, not even a whole person. However we have 3 here which is obviously higher than 0.5% (it comes out to be 1.9%). But what does that actually mean? It means that if you are AB- you are 380% more likely to have Crohn's than expected. Ok but 3 is such a small sample size, 1 or 2 more votes could effect it in either direction. Well what about O-? 22 people, or 13.92% of the 158 should be enough to get an estimate.

O- accounts for 4.3% of the population, which would be 6.79 people in our 158 member population, far below the 22 people we actually have. Making O- 324% more likely to have Crohn's, and since it is the most common RH Negative blood type, that makes O- most likely to have Crohn's, by a fairly large margin. In fact, in EVERY case, RH- is more likely to have Crohn's than the RH+ counterpart.

You can see in the table I put together (attached below) that RH+ either matches up with the worldwide %, or is under it, meaning if you are RH+ you are actually LESS likely to have Crohn's then we would expect based on blood type distribution. And the opposite with RH- in every case.

For a more visual perspective, take a look at this chart (attached below).

Note that aside from AB+ which is just .6% higher (9 people instead of 8) and so I didn't include it as being significant. I filtered out any numbers that were either 1% or less, higher or lower than baseline. What this chart shows is that the only times the actual Crohn's rate is higher than average is with RH- (notice how much higher O- is than all others), and the only times the actual Crohn's rate is lower than average is with RH+. Those who are B+ are the least likely to have Crohn's.

Now I'll admit that I am not a statistician but rather a programmer so it's possible I've made some mistakes in my math. Feel free to check my work, but I'm confident that I've shown that there is in fact a correlation between RH- and Crohn's, and more specifically that the largest correlation is with O-.