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What is a CI?
  1. Jane Clarke
  1. Correspondence to Jane Clarke
    , Department of O&G, University of Auckland, 4 Prime Rd, Grey Lynn Auckland, Auckland 1021, New Zealand; janeclarkehome{at}

Statistics from

The theory

When reading a research report, the range of the CI provides assurance (or confidence) regarding how precise the data are. CIs are calculated at a confidence level, for example 95%. This level is predetermined by the researcher. Confidence 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 reflect the whole population.

CIs are considered a more useful measure than p values, which only reflect a level of statistical significance.1(p values were discussed in a previous Research Made Simple paper.2)

The concept

A CI is a numerical range used …

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