Perioperative The period from admission through surgery until discharge, encompassing the preoperative and postoperative periods. Placebo A fake (or dummy) treatment given to participants in the control group of a clinical trial. It is indistinguishable from the actual treatment (which is given to participants in the experimental group). The aim is to determine what effect the experimental treatment has had over and above any placebo effect caused because someone has received (or thinks they have received) care or attention. Polypharmacy The use or prescription of multiple medications. Posterior distribution In Bayesian statistics this is the probability distribution for a statistic based after combining established information or belief (the prior) with new Chronic Heart Failure Glossary NICE 2018. All rights reserved. Subject to Notice of rights. ISBN: 978-1-4731-3093-7 Term Definition evidence (the likelihood). Positive predictive value (PPV) In screening or diagnostic tests: A measure of the usefulness of a screening or diagnostic test. It is the proportion of those with a positive test result who have the disease, and can be interpreted as the probability that a positive test result is correct. It is calculated as follows: TP/(TP+FP) Postoperative Pertaining to the period after patients leave the operating theatre, following surgery. Post-test probability In diagnostic tests: The proportion of patients with that particular test result who have the target disorder (post-test odds/[1 plus post-test odds]). Power (statistical) The ability to demonstrate an association when one exists. Power is related to sample size; the larger the sample size, the greater the power and the lower the risk that a possible association could be missed. Preoperative The period before surgery commences. Pre-test probability In diagnostic tests: The proportion of people with the target disorder in the population at risk at a specific time point or time interval. 