Confidence Intervals

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Confidence Intervals

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Understanding Confidence Intervals

Java Applets

The concept of a confidence interval is quite difficult for beginning statistics students, and sometimes for beginning statistics teachers! For example, assume that our population parameter of interest is the population mean. What is the meaning of a 95% confidence interval in this situation?

Many students want to say that a 95% confidence interval means that there is a 95% chance that the confidence interval contains the population mean. But any particular confidence interval either contains the population mean, or it doesn’t. The confidence interval shouldn’t be interpreted as a probability.

The correct interpretation is based on repeated sampling. If samples of the same size are drawn repeatedly from a population, and a confidence interval is calculated from each sample, then 95% of these intervals should contain the population mean.

Understanding Confidence Intervals is an activity which helps students understand confidence intervals. The activity requires a TI-83 graphing calculator.

STEPS

The STEPS modules are a collection of hypertext-based tutorials covering a wide range of statistics topics, including confidence intervals. Visit the STEPS page for further information and a list of the modules available.

Confidence Intervals Java Applet

The applet helps students understand confidence intervals. Each of the 50 lines on the graph represents one confidence interval for the mean.