Posted by **Katerina** on Sunday, November 28, 2010 at 10:52am.

A Swedish study used 1360 patients who had suffered a stroke. The study

randomly assigned 684 patients to receive a placebo treatment and the rest to receive an

aspirin treatment. Out of those who received the placebo treatment, 28 died due to heart

attack in 3 years, whereas 18 of those who received the aspirin treatment died due to heart

attack in the same period.

Obtain a 95% confdence interval for the difference in the chance of death due to heart

attack between the two groups.

So for the placebo group n=684 and 28 died so the proportion that died is 0.041.

For the aspirin group n= 676 and 18 died. So the proportion that died is 0.027.

Since we're looking for the 95% confidence level the zscore would be 1.96.

I'm not sure how I would find the standard deviation though.

But once I have a value for the standard deviation I could find the margin of error and the interval for the chance of death.

Or do we even need to find the SD for this question?

I was also thinking I might have to calculate the probabilty of someone dying in either group? But I'm not sure how to do this. And does the fact that the patients died within 3 years have any relevance?

Thanks for your help!

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