If you are given summary data and asked to find a confidence interval, it is relatively easy using StatCrunch. Here is a typical problem: In this problem, you are told to use the t-distribution, but… Confidence Interval for a Mean using StatCrunch
For the present, yes, the degrees of freedom you need to find values of t are going to be equal to n-1. That’s all you need to know for the midterm. Later in the course,… Degrees of Freedom
Consider the following problem:
The grade point averages for 12 randomly selected students are shown in the table below. Find the 99% confidence interval around the population mean, ยต. Assume the population is normally distributed.
Solution:
This is a small sample, n < 30, and we do not know sigma. Although small samples generally are t-distributions, the deciding factor for BUS233 is the lack of the population standard deviation, sigma. Therefore, use the t-distribution.
The Excel solution is:Single-Sample, Confidence Interval for a Mean using t-distribution