Research results are based on probabilities and so there is a margin of error, called the ‘confidence interval’. It is important for the confidence interval to be reported. A research result without this information may be misleading.
The observed difference in outcomes is the best estimate of how relatively effective interventions are (or would be, if the comparison were made in many more people). However, because of the play of chance, the true difference may be larger or smaller. The confidence interval is the range that is likely to include the true effect, after taking account of the play of chance. Although a confidence interval (margin of error) is more informative than a p-value, the latter is often reported. P-values are often misinterpreted to mean that interventions have or do not have important effects.
Understanding a confidence interval may be necessary to understand the reliability of an estimated intervention effect.
BEWARE of being misled by p-values.
REMEMBER: Whenever possible, consider confidence intervals when assessing estimates of intervention effects.