Question

You are interested in interviewing people who own both a cat and a dog. The estimated incidence rate in the population is 17%. You expect a survey completion rate of 45%.

What final sample size would be required to obtain a statistical estimate of a parameter with an expected proportion of 50% within +/- 3% with 95% confidence?

What initial sample size (e.g., how many invites) is required to obtain the necessary final sample size for analysis?

Answer 1

Solution:

Given that:

E= 0.03

= 0.50

1 - = 1 - 0.50= 0.50

At 95% confidence level the z is ,

= 1 - 95% = 1 - 0.95= 0.05

/ 2 = 0.05/ 2 = 0.025

Z/2 = Z0.025 = 1.96

sample size = ( Z/2 / E)2 * * (1 - )     

   = ( 1.96/ 0.03 )2 *0.50*0.50

                   = 1067.1

sample size  = 1067