First post and I'm afraid I'm so out of my depth I don't even know if my title is correct. I am very new to statistics and have been struggling through but am now completely stuck. Any help would be massively appreciated. My basic question is

**what test can I use to determine significance between two cohorts and a binary variable?**

Some background: I am trying to publish a research paper on what catheters (tube to wee through) are placed in patients following a TURP - resection of the prostate gland. Common practice is to put a three way catheter (3WC), which is done everywhere except my hospital, where we put a two-way catheter (2WC). We have collected data for a decade and our outcomes look equivalent to other centres and in some aspects better - and it's cheaper to do it our way too.

So, over the decade we have placed both two- and three-way catheters so we have two cohorts in our own data set to compare - that I think I've done fine. The next step is comparing data from our set to an externally published source. The current variable I am looking at is:

What proportion of patients required blood transfusion intra-/post-operatively. So looking at the 2WC cohort of my patients: 3/601 (0.17%) required transfusion, in the externally published cohort of 3WC patients, 0/247 required transfusion. I tried a Chi-square calculator but that came back saying you can't use zero as a value? (I don't understand why?).

I understand that these numbers are tiny and therefore will have limited significance but I would like to show that with a massive

*p*number somehow.

Any help would be massively appreciated, many thanks in advance for anyone that takes the time.

L