Confidence Interval for the Population Mean
Technology C onfidence I ntervals
for
297 
Template 7.1B M eans
with
s U nknown
Figure 7.7 presents the case where the standard deviation is unknown and the sample is taken from a population that is normally distributed: we use the t-statistic. The sample size, the sample mean, and the sample standard Âdeviation are entered in cells C17, C18, and C19 respectively. The confidence interval is automatically computed for different levels of confidence (cells B23:B26).
Example 7.6 A sample of hospitals in 20 regions of Saudi Arabia yielded a national average length of stay for inpatients of 3.8 days, with a standard deviation of 0.96 days. Assume that the distribution is normal. Construct a 95% confidence interval for the length of stay in Saudi hospitalsiii.
iii Source: 2009
Health Statistical Yearbook
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