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How do I interpret a confidence interval?
Author(s) -
O'Brien Sheila F.,
Yi Qi Long
Publication year - 2016
Publication title -
transfusion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.045
H-Index - 132
eISSN - 1537-2995
pISSN - 0041-1132
DOI - 10.1111/trf.13635
Subject(s) - confidence interval , sample size determination , statistics , range (aeronautics) , population , sample (material) , statistical significance , mean difference , interval (graph theory) , population mean , clinical significance , mathematics , medicine , demography , combinatorics , physics , materials science , environmental health , estimator , sociology , composite material , thermodynamics
A 95% confidence interval (CI) of the mean is a range with an upper and lower number calculated from a sample. Because the true population mean is unknown, this range describes possible values that the mean could be. If multiple samples were drawn from the same population and a 95% CI calculated for each sample, we would expect the population mean to be found within 95% of these CIs. CIs are sensitive to variability in the population (spread of values) and sample size. When used to compare the means of two or more treatment groups, a CI shows the magnitude of a difference between groups. This is helpful in understanding both the statistical significance and the clinical significance of a treatment. In this article we describe the basic principles of CIs and their interpretation.