Question

People were polled on how many books they read the previous year. How many subjects are needed to estimate the number of books read the previous year within one book with

95​%

​confidence? Initial survey results indicate that

sigmaσequals=13.4

books.

A

95 %

confidence level requires ____ subjects.

Answer 1

Solution :

Given that,

standard deviation = = 13.4

margin of error = E = 1

At 95% confidence level the z is ,

= 1 - 95% = 1 - 0.95 = 0.05

/ 2 = 0.05 / 2 = 0.025

Z_/2 = Z_0.025 = 1.96

Sample size = n = ((Z_/2 * ) / E)²

= ((1.96 * 13.4) / 1)²

= 689.79 = 690

Sample size = 690

95 % confidence level requires 690 subjects .