A survey is planned to determine the mean annual family medical expenses of SVSU staff and faculty. The staff conducting this research wish to be 95% confident that the sample mean is correct to within $50 of the population mean. A previous study indicates the standard deviation is approximately $294.
How large of a sample is necessary?
Solution :
Given that,
standard deviation = = 294
margin of error = E = 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 = 1.960
Sample size = n = ((Z/2 * ) / E)2
= ((1.960* 294) / 50)2
= 132.82
= 133
Sample size = 133
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