Chi2 test


New Member

I have a problem with this test. We had to write report on prevalence of infected snails at two seasides and base it on Chi2 test calculations. I just got the report back and apparently all the tests i did were wrong according to my tutor and i dont know why. e.g. we had to find out if there was a significant difference between numbers of infected snails at Martin Bay and Thomas Bay. The problem is that the total numbers of collected and examined snails were different for both bays. The numbers were 58 infected/ 647 total and 43 infected/857 total. What the tutor wanted me to do was to take the average of 43+ 58 and that would be my expected result for both bays. But it seems to me that this method would produce unreliable results as the sample sizes were so different. Can anyone explain that to me, many please!!! cuz im totally lost :confused:


TS Contributor
I agree with you. If you do a chi-squared test, you should get a table that looks like the attached image.


New Member
thanx a lot :D
thats exactly what i had, but she crossed it out and put a big question mark next to it... i guess i will have to talk to her then :)