What is the 95-percent confidence interval? The most common size for a confidence interval is 95 percent. Use it as a comparison for the other confidence intervals. What is the 90-percent confidence interval? It is narrower than the 95-percent confidence interval, so we have less confidence that it includes the true value. But note that it isn't that much smaller. Slide the scrollbar to the far left to get the 50-percent confidence interval. With only a 50-50 chance that the interval includes the true value, it can be much narrower. Does it seem a lot different than the 95-percent confidence interval? What is the 99-percent confidence interval? It is wider than the 95-percent confidence interval so we have more confidence that it includes the true value. Is the original null hypothesis of guessing, an expected mean of 10, contained in the 99-percent confidence interval? What is the largest confidence interval that does not include the original null hypothesis of guessing, an expected mean of 10? What is the 99.9-percent confidence interval? If we wanted to be absolutely certain that we included the true mean, we would want the 100-percent confidence interval. How wide would it be?