attrition—in the context of research studies, refers to the gradual loss of study participants, some percentage of whom often drop out.
benefit-cost analysis—a method of economic analysis in which both costs and outcomes of an intervention are valued in monetary terms, permitting a direct comparison of the benefits produced by the intervention with its costs (also referred to as cost-benefit analysis).
cost-effectiveness analysis—a method of economic analysis in which outcomes of an intervention are measured in nonmonetary terms. The outcomes and costs are compared with both the outcomes (using the same outcome measures) and the costs for competing interventions, or with an established standard, to determine if the outcomes are achieved at reasonable monetary cost.
discount rate—a factor used to estimate future costs or the value of future benefits at the current equivalent value, used with the goal of attempting to take into account likely changes in valuation, opportunity costs, and other factors.
effect size—the magnitude of results (or effects on participants) of a particular treatment or intervention that is being studied.
interrupted time series study—is a type of quasi-experiment in which measures on a sample or a series of samples from the same population are obtained several times before and after a manipulated event or a naturally occurring event.
Monte Carlo simulation—the repeated drawing of uncertain parameters from assumed distributions to produce a distribution of possible outcomes. In benefit-cost analysis, Monte Carlo simulation is used to translate uncertainty in predicted resource use, impacts, and their monetizations into a distribution of predicted net benefits.
opportunity cost—the value of alternatives not chosen, calculated as part of an analysis of the costs of the alternative that was chosen.
quasi-experimental design—an experiment designed to produce evidence of causality when randomized controlled trials are not possible, using alternative statistical procedures to compensate for nonrandom factors.
randomized controlled trial—an experiment in which the participants are assigned by chance either to receive the intervention or treatment being studied or not to receive it, so the results can be compared across statistical identical groups. When this is done with a large enough number of participants, any differences among them that might influence their response to the treatment will be distributed evenly.
regression discontinuity design—a quasi-experimental analysis that can be used in program evaluation when randomized assignment is not feasible. It is based on the assumption that individuals who fall just above or below a cutoff point on a particular scale are likely to be similar, so that this group can be treated as varying randomly.
shadow price—the true value or cost of the results of a particular decision, as calculated when no market price is available; a dollar value attached to an opportunity cost.
standard error—used to refer to the standard deviation of various sample statistics such as the mean or median. The smaller the standard error, the more representative the sample will be of the overall population.