Sample size calculation for prospective observational study studying outcome of an intervention?

Hello everyone,
I am submitting proposal for thesis and I need help with the sample size calculation.

My study is: to study the outcome of "x" intervention in "y" disease
The prevalence of disease is 2.6%.

How do I calculate the needed sample size? What else information do I need from the previous study?

Thanks in advance.


Less is more. Stay pure. Stay poor.
What is the intervention and what is the outcome? How are they formatted? Traditionally X represents intervention and y the dependent variable (outcome).
Functional outcome is a score and intervention is a type of surgery and disease is a fracture. The prevalence of disease is around 2.6%.


Less is more. Stay pure. Stay poor.
You have three things here. Surgery is the intervention, what do the other two variables represent? How is score formatted and what is its distribution?
Hi hlsmith, I mean:

I need to study the outcome of an intervention in a disease. I will be doing a prospective observational (longitudinal) study in a single cohort (I am not sure if i'm correct - I mean, I will be taking only a single group of diseased undergoing the proposed intervention). The prevalence of the disease is ~2.6%. The mean +/- SD of the measured outcome in previous study is 253 +/- 9.
So, How will I proceed further with the sample size calculation?
Any help will be greatly appreciated.