In: Statistics and Probability
Suppose you monitor quality assurance for a local hospital and want to estimate the average length of stay (LOS) at your hospital. You take a random sample of 30 patients and find that the average LOS is 3.4 days with a sample standard deviation of 1.2 days. What is the 99% confidence interval for the population average length of stay?
Solution :
Given that,
Point estimate = sample mean = = 3.4
sample standard deviation = s = 1.2
sample size = n = 30
Degrees of freedom = df = n - 1 = 30 - 1 = 29
At 99% confidence level the t is ,
= 1 - 99% = 1 - 0.99 = 0.01
/ 2 = 0.01 / 2 = 0.005
t /2,df = t0.005,29 = 2.756
Margin of error = E = t/2,df * (s /n)
= 2.756 * (1.2 / 30)
E = 0.6
The 99% confidence interval estimate of the population mean is,
- E < < + E
3.4 - 0.6 < < 3.4 + 0.6
2.8 < < 4.0
( 2.8,4.0 )
The 99% confidence interval is (2.8 , 4.0)