Confidence intervals

Draw sample after sample and see how often the interval catches the population mean.

Every sample gives its own confidence interval. The vertical line is the true population mean. Press +1 to draw a sample, then +50 or +500 to draw many, and see how often the intervals catch it.

Open the simulator in a full window

Things to try

Each link opens the simulator ready to go. Before you press a button, predict what will happen.

What does a confidence interval promise?

• 100 intervals. The population mean never moves. The intervals do. About 95% of them catch it. Then raise n and watch them narrow.
• When H₀ is false. An interval that leaves out the H₀ mean means the same as rejecting H₀. Look at how often that happens, then compare it with the power for the same effect and sample size.

Credit

This simulator was written for EDUC 15. This view was inspired by the confidence interval visualization by Kristoffer Magnusson at R Psychologist.