Instructor: Hello students,
and welcome to Biostats ER Chapter eight, Example nine.
In this example, we will learn how to calculate sample size
for two-independent samples dichotomous data
to determine confidence interval.
This problem is not from our textbook,
and as always, I'm going to read the problem first.
The issue here is that we have a treatment group
and a placebo group who have reported on pain relief.
In the placebo group, we have 20% pain relief reported,
and in the treatment group we have 10% pain relief reported.
Now we want to determine what sample size do we need
to generate a 90% confidence interval
for the difference between these two groups
that is at most 5% from the true mean.
So here I have summarized some
of the information that is provided.
And then I have provided you with the formula
that we need to solve this problem.
So once we start inserting the values here,
P1 is 0.2.
1 - P1 is 0.8.
P2 is 0.1,
and 1 - P2 is 0.9.
And the Z value here is
1.645 and the margin of error here is 0.05.
So after we insert all these values
and perform the calculation,
our answer here is 270.6,
and we always round up for sample size calculation
and that gives us 271.
So for each group, we need 271 subjects.