In: Statistics and Probability
An economist wants to estimate the mean per capita income (in thousands of dollars) for a major city in California. Suppose that the mean income is found to be $23.1 for a random sample of 3231 people. Assume the population standard deviation is known to be $11.8. Construct the 95% confidence interval for the mean per capita income in thousands of dollars. Round your answers to one decimal place.
Solution :
Given that,
= 23.1
= 11.8
n = 3231
At 95% confidence level the z is ,
= 1 - 95% = 1 - 0.95 = 0.05
/ 2 = 0.05 / 2 = 0.025
Z/2 = Z0.025 = 1.960
Margin of error = E = Z/2* (/n)
= 1.960 * (11.8 / 3231 )
= 0.4
At 95% confidence interval estimate of the population mean is,
- E < < + E
23.1 - 0.4 < < 23.1 + 0.4
22.7 < < 23.5
( 22.7, 23.5 )