Instructor: Hello students, welcome to Biostat ER,
chapter eight, example seven.
In this example, we will learn how to calculate sample size
for one-sample dichotomous data
to determine confidence interval.
The problem here is not from our textbook,
and the issue here is that we have a new policy
implemented in a private practice
and we would like to know what proportion of patients
are in favor of this new policy.
With 95% confidence, we want to state
that our estimate is within 3%
of the true proportion of patients
who are in favor of the new policy.
So, how many subjects are required?
As always, I have summarized the information here
and I have also stated the formula.
Now, before we can move forward,
we need to determine the value of the P here.
Sometimes we can determine this P value from the literature
or have an established value.
However, here that is not feasible as this is a new policy.
Because we always want to be conservative
in sample size calculation,
we want to utilize a P value
that will give us the largest sample size
within the margin of error we want to remain,
and that value is 0.50.
So, for the initial part of the calculation,
as we insert 0.50, we obtain a value of 0.25.
I encourage you to experiment with different P values
to determine if you can obtain a value larger than 0.25.
The Z value here will be 1.96,
and once we insert all these values and perform the algebra,
we will get 1066.02, and as always, we will round up.
So we will need 1067 subjects.