Question

Suppose that the recovery period, in days, for patients having back surgery is normally distributed with an unknown mean and standard deviation. The recovery period lengths of 39 randomly sampled back surgery patients are used to estimate the mean of the population. Use Excel to find the t-score that should be used to calculate the 99% confidence interval for the population mean.

Round your answer to three decimal places.

Answer 1

Answer: 2.712

Explanation:

2.712

The sample used was 39 patients, so n=39.

To find the degrees of freedom:

df=n−1=39−1=38

The confidence level is given in the scenario: 99%.

So,α=1−CL=1−0.99=0.01

But we want to use the value for α2, which is 0.012=0.005.

Using the table, we need to find the row for 38 degrees of freedom, and the column for t0.005. So, the t-score we would use to find the 99% confidence interval is 2.712.

We could also use a calculator and input 1−α2=0.995 and the degrees of freedom into invT, in which case we would enter invT(0.995,38).