Confidence Intervals

Point Estimates'

The sample mean is the best point estimate of the population mean.

Confidence Intervals

Confidence intervals give a plausible range of values for a population parameter

Confidence intervals also give information about the precision of an estimate

A confidence interval estimate of a parameter consists of an interval of numbers along with a probability that the interval contains the unknown parameter

Calculation of a Confidence Interval

Depends upon three factors

• The point estimate of the population (often a mean)

• The level of confidence (often 95%)

• The standard error

Confidence Interval Summary

Gives a range of possible population parameters

Sample CI will contain the parameter 95% of the time

If mean difference CI contains 0 → not significant

If mean difference CI does not contain 0 → significant