1. A researcher wants to estimate the percentage of all adults that have used the Internet to seek pre-purchase information in the past 30 days, with a tolerable sampling error (E) of 0.03 and a confidence level of 97.5%.  If secondary data indicated that 25% of all adults had used the Internet for such a purpose, what is the sample size?  See page 312 of your text book.

Level of Significance = 0.025

z Score of ½ of Level of Significance = 2.24

Sampling Error, E = 0.03

σ = 0.75

n = ( z2 * σ2 ) / E2

n =  1046.64 = 1047

Sample size = 1047

 

  1. A researcher wants to estimate a population mean.  The level of tolerable sampling error is 0.2 of a purchase occasion, with a confidence level of 95.44%.  If the estimated population variance is 5 for the most important question in the study, what is the desired sample size? See page 310 of your text book.

From the z table, z score for 95.44% is 1.69.

n = ( z2 * σ2 ) / E2 = (1.692 x 52 ) / 0.22 = 1785

1) at 95.44% confidence, Z = 2

 

2) sample means formula is appropriate

 

3) Variance = 5

 

4) Tolerable Error = .2

 

5) Computed Sample size of 500.