Instructor: Hello students and welcome
to Biostat ER chapter eight, example five.
In this example, we will learn how to calculate sample size
for two-independent samples, continuous outcome,
to determine confidence interval.
This example is from our textbook.
So this is problem 11
and first I'm going to read the problem.
"We wish to design a study to assess risk factors
for stroke and dementia.
There are two primary outcome measures.
The first is a measure of neurologic function.
Patients with normal function typically score 70
with a standard deviation of 15.
The second outcome is incident stroke.
In patients over the age of 65,
approximately 40% developed stroke over 25 years.
How many participants over the age of 65
must be enrolled to ensure the following?
That the margin of error in a 95% confidence interval
for the difference in mean neurologic function scores
between men and women does not exceed two units."
So first here we have to
select the correct formula, and I have
provided you with the formula here.
And after that we have to insert the values
into our formula, which are provided in our problem.
So the Z value here is going to be 1.96 again
because it is 95% confidence interval
and we have used the Z value right now multiple times.
The sigma here is going to be 15
as it is provided in our problem.
And I've highlighted in yellow.
And then the denominator here is going to be two again,
which is provided to us in our problem.
And again, I have highlighted that value in yellow.
So once we insert all these values
and we perform the algebra, we get 432.2.
So the sample size here is going to be 433 for men,
and 433 for women and that is what we will need.
And again, we always round up for sample size calculation.
That's why from 432.2, we will round it up to 433
and we will require an equal sample size for both men
and women to perform the calculation
for the confidence interval.
(mouse clicking)