There is always some uncertainty in research. This is because a small group of patients (called the sample) is studied to predict the effects in the wider population who may eventually use the treatment. The confidence interval (CI) shows the amount of uncertainty. It gives a range of results from the study that is likely to include the ‘true’ value for the population. The CI is usually stated as ‘95% CI’, which means that the range of values have a 95 in 100 chance of including the ‘true’ value. For example, a study may state that ‘based on our sample findings, we are 95% certain that the ‘true’ population blood pressure is not higher than 150 and not lower than 110; thus 95% CI is 110 to 150’. HTAI
