Medical stats - which statistical test to use? Stuck!

Dear all,

I need some help with determining what statistical test to use for the following data.

I have a column for age of patient and I want to compare this statistically with another column where it is stated YES if a infection occured or NO if no infection occured. I have grouped the ages into under 25, 26-35, 36-45......etc and I want to see if there is a statisically significant variation beween the different age groups and the frequency of infections (yes/no) in each age group.

For example

under 25: 23 no infection, 3 yes infection
26-35: 18 no infection, 2 yes infection
36-45: 22 no infection, 0 yes infection
46-55: 28 no infection, 4 yes infection
56-65: 3 no infection, 15 yes infection
66-75: 23 no infectin, 2 yes infection

Similarly, I have a column of surgical procedures and I want to also compare this statisically with a column for infection (yes/no) to see if there is a statistical variation between the 30 surgical procedures and the number of infections.

Also , I have a column of 23 countries of residence and I would like to compare this statically with the number of infections.

Could someone kindly assist me with this? Which stats test should I use?

Many thanks!


New Member
For the age/infection as you have them organized - into age groups - chi-square goodness of fit would work, with age groups as the categories and "proportion having an infection" as the proportions.

Or if you used age/infection and did not group the ages, you could do logistic regression with age as the predictor and infection (yes/no) as the DV.

You didn't give a lot of detail about the surgical procedures and countries of residence variables, but they both sound like nominal variables in which case chi-quare GOF test works for those analyses as well.
Dear bruin,

Thank you for your reply.

With regards to Chi square goodness of fit, would it still be appropriate if more than 20% of variables had a frequency of less than 5?

With regards to procedure and country of origin the data is like.


Upper GI surgery: 123 no infection 5 yes infection
Lower GI surgery: 130 no infection 3 yes infection
Urology surgery: 46 no infection 1 yes infection
Orthopaedic surgery: 8 no infection 0 yes infection

Argentina 1 no infection 0 yes infection
Burma 2 no infection 0 yes infection
Cyprus 6 no infection 1 yes infection
UK 128 no infection 6 yes infection
America 60 no infection 3 yes infection

There are several frequencies that may be 0 or small numbers.

Would a Chi squared GOF test be okay?

Thank you!