What is a CI?

The theory When reading a research report, the range of the CI provides assurance (or confi dence) regarding how precise the data are. CIs are calculated at a confi dence level, for example 95%. This level is predetermined by the researcher. Confi dence levels are usually calculated so that this percentage is 95% although others 90%, 99%, and 99.9% are sometimes applied. Researchers collect numerical data and then apply statistical tests. An example of a common statistical test applied by researchers is the mean which is then used to approximate the average for an entire population. CIs provide an indication of how reliably these results refl ect the whole population. CIs are considered a more useful measure than p values, which only refl ect a level of statistical signifi cance.1(p values were discussed in a previous Research Made Simple paper.2)