Contents
Can a confidence interval contain 0?
If your confidence interval for a difference between groups includes zero, that means that if you run your experiment again you have a good chance of finding no difference between groups.
What does it mean if your confidence interval includes 0?
Zero is the null value of the parameter (in this case the difference in means). If a 95% confidence interval includes the null value, then there is no statistically meaningful or statistically significant difference between the groups.
Can confidence intervals be negative?
If the t value is negative, then the confidence intervals will also contain negative numbers. So long as the confidence interval does not cross zero (does not contain one positive and one negative number), it will be much easier to interpret it if you use the absolute value of the confidence interval.
How to calculate the 95% confidence interval?
On the other hand, you can still compute a confidence interval for this data. The simplest formula uses the rule of three. If you observe n patients, and none of these patients have an adverse event, then a 95% confidence interval for the probability of an adverse event goes from zero to 3/n.
When to use a zero to zero confidence interval?
When you have a reasonable mixture of events and non-events, then this approximation is fine. But if the number of events or non-events is small (say less than five), then the normal approximation is a lousy approximation. So your friend is wrong if he believes in his zero to zero confidence interval.
What is the upper confidence limit for zero events?
This confidence interval used the classical formula and was clearly invalid since it went from zero to zero. Professor Mean explains the rule of three: when you have zero event out of n, a 95% upper confidence limit for the true proportion is 3/n.
The confidence interval does not reflect the variability in the unknown parameter. Rather, it reflects the amount of random error in the sample and provides a range of values that are likely to include the unknown parameter.