There are several types of economic evaluation: cost benefit analysis, cost consequences analysis, cost-effectiveness analysis, cost-minimisation analysis and cost utility analysis. They use similar methods to define and evaluate costs, but differ in the way they estimate the benefits of a particular drug, programme or intervention. Effect (as in effect measure, treatment effect, estimate of effect, effect size) A measure that shows the magnitude of the outcome in one group compared with that in a control group. For example, if the absolute risk reduction is shown to be 5% and it is the outcome of interest, the effect size is 5%. The effect size is usually tested, using statistics, to find out how likely it is that the effect is a result of the treatment and has not just happened by chance (that is, to see if it is statistically significant). Effectiveness How beneficial a test or treatment is under usual or everyday conditions, compared with doing nothing or opting for another type of care. Efficacy How beneficial a test, treatment or public health intervention is under ideal conditions (for example, in a laboratory), compared with doing nothing or opting for another type of care. Epidemiological study The study of a disease within a population, defining its incidence and prevalence and examining the roles of external influences (for example, infection, diet) and interventions. dimensions) A standardised instrument used to measure health-related quality of life. It provides a single index value for health status. Evidence Information on which a decision or guidance is based. Evidence is obtained from a range of sources including randomised controlled trials, observational studies, expert opinion (of clinical professionals or patients). Exclusion criteria (literature review) Explicit standards used to decide which studies should be excluded from consideration as potential sources of evidence. 