Confidence Intervals

The larger the interval range, the more the confidence percentage. People usually set the confidence percentage first and then find the range.

Confidence interval is plus or minus the z score of alpha/2 multiplied by standard error (sigma/square root of n). You can substitute t for z and sigma for s, if you do not know sigma.

"95% confident that the interval includes the parameter." Avoid the "parameter falls between the interval."

Comparing Means With Confidence Intervals

Do the intervals overlap? If yes, no statistical difference. That's it. Replaces Ho testing for between groups and repeated measures.

Confidence Interval for proportions/percentages/pearson r is not tested in this course.

Confidence Interval applications:
1. Estimate population mean based on sample mean when sigma is known (z)
2. Estimate population mean based on sample mean when sigma is not known (t)
3. Test for statistically significant difference between means (do the intervals overlap?)
4. and 5. Test for statistically significant difference between means (does interval contain zero?) for (4) between groups and (5) repeated measures