From the course: Complete Guide to Excel Statistics with Copilot
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Creating confidence intervals in Excel: Means
From the course: Complete Guide to Excel Statistics with Copilot
Creating confidence intervals in Excel: Means
- [Instructor] Let's now create confidence intervals for mean. So instead of looking for the proportion of homes that have dogs, here we're interested in the average weight of dogs in the city. Suppose we gather a random sample of 25 dogs from the city. The average weight of dogs in this sample is about 35 pounds. And suppose you're given one other important piece of information, you're told the standard deviation of the weight of dogs in the city is 15. Please note that is the population standard deviation. Here are the formulas for the upper and lower limits. In the formula's X-bar is the mean of our sample, 36 pounds. And let's say we're going to create a 95% confidence interval. We've used that in a previous video. We know that the critical value, the Z-score, is 1.96. So now we need to find the standard error. The formula for the standard error is sigma, our population standard deviation, 15, divided by the square root of N, the sample size, 25. The square root of 25 is five, so…
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