ABSTRACT
Confidence intervals are used to estimate how far away the population mean is likely to be, with a given degree of certainty. This technique is called estimation. The chapter shows diastolic blood pressure measurements taken from a sample of 92 patients with diabetes. The mean diastolic blood pressure is 82.696 mmHg, with a standard error of 1.116. A 95% confidence interval will indicate a range above and below 82.696 mmHg in which the population mean will lie, with a 95% degree of certainty. In other words, a ‘95% confidence interval’ is the interval which will include the true population value in 95% of cases. It should therefore be reasonably representative of patients with diabetes, so long as the sample was randomly selected. Increasing the sample size will usually result in a narrower confidence interval. There are different formulae for calculating confidence intervals and standard error in other situations.
