The wider an interval is, the more uncertainty there is in the estimate. What is a confidence interval and "confidence level"Ī confidence interval is defined by an upper and lower boundary (limit) for the value of a variable of interest and it aims to aid in assessing the uncertainty associated with a measurement, usually in experimental context, but also in observational studies. If your experiment involves more than one treatment group or involve more than one outcome variables you need a more advanced calculator which corrects for multiple comparisons and multiple testing. Also, you should not use this confidence interval calculator for comparisons of more than two means or proportions, or for comparisons of two groups based on more than one metric. Doing otherwise means being guilty of optional stopping (fishing for significance) which will result in intervals that have narrower coverage than the nominal.
Warning: You must have fixed the sample size / stopping time of your experiment in advance. The Z-score ( z statistic) and the p-value for the one-sided hypothesis (one-tailed test) will also be printed when calculating a confidence interval for the difference between proportions or means, allowing you to infer the direction of the effect. For means data the calculator will also output the sample sizes, means, and pooled standard error of the mean.
It works for comparing independent samples, or for assessing if a sample belongs to a known population. The confidence interval calculator will output: two-sided confidence interval, left-sided and right-sided confidence interval, as well as the mean or difference ± the standard error of the mean (SEM). Copy-pasting from a Google or Excel spreadsheet works fine. If entering means data, make sure the tool is in "raw data" mode and simply copy/paste or type in the raw data, each observation separated by comma, space, new line or tab. 10%) or just the raw number of events (e.g. If entering data for a CI for difference in proportions, provide the calculator the sample sizes of the two groups as well as the number or rate of events. If you are interested in a CI from a single group, then to calculate the confidence interval you need to know the sample size, sample standard deviation and the sample arithmetic average. You can select any level of significance you require. It uses the Z-distribution (normal distribution). You can also calculate a confidence interval for the average of just a single group. height, weight, speed, time, revenue, etc.), or the relative difference between two proportions or two means. conversion rate or event rate) or the absolute difference of two means (continuous data, e.g. This confidence interval calculator allows you to perform a post-hoc statistical evaluation of a set of data when the outcome of interest is the absolute difference of two proportions (binomial data, e.g.
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