Confidence Interval for a Population Mean (t-interval) Calculator
The t-interval provides a range of values calculated from sample data that is likely to contain the true population mean when the population standard deviation is unknown.
Formula first
Overview
This statistical method utilizes the Student's t-distribution to account for the additional uncertainty introduced by estimating the population standard deviation using the sample standard deviation. It is the preferred method for small sample sizes or when the population variance cannot be assumed known, provided the underlying population is approximately normal.
Symbols
Variables
= Sample Mean, = Critical t-value, s = Sample Standard Deviation, n = Sample Size, ME = Margin of Error
Apply it well
When To Use
When to use: Use this interval when you need to estimate a population mean from a small sample (n < 30) or when the population standard deviation is unknown.
Why it matters: It allows researchers to quantify the reliability of their estimates in real-world scenarios where data is limited and population parameters are inaccessible.
Avoid these traps
Common Mistakes
- Using the Z-score instead of the T-score when the population standard deviation is unknown.
- Forgetting to subtract 1 from the sample size when determining degrees of freedom.
One free problem
Practice Problem
A sample of 10 students has a mean study time of 15 hours with a sample standard deviation of 3. Using a t-score of 2.262 for 95% confidence, find the margin of error.
Solve for: margin
Hint: Multiply the t-score by the standard error, which is s divided by the square root of n.
The full worked solution stays in the interactive walkthrough.
References
Sources
- Moore, D. S., McCabe, G. P., & Craig, B. A. (2017). Introduction to the Practice of Statistics (9th ed.). W. H. Freeman and Company.
- OpenStax. (2018). Introductory Statistics. Rice University.
- Moore, D. S., McCabe, G. P., & Craig, B. A. (2017). Introduction to the Practice of Statistics.
- OpenStax, Introductory Statistics.
- Wackerly, D., Mendenhall, W., & Scheaffer, R. L. (2008). Mathematical Statistics with Applications.