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.

economy of scale—advantages that accrue when a project is conducted on a larger scale than initially, which result from opportunities to use resources more efficiently and to reduce costs.

effect size—the magnitude of results (or effects on participants) of a particular treatment or intervention that is being studied.

independent variable—one of the characteristics of an experiment’s subjects that are considered in the study design, such as, for example, the age and gender of the participants in an early childhood program.

intent-to-treat—the group of study participants randomly selected to receive the intervention being studied.

multivariate regression model—a statistical procedure for examining experimentally the relationship among several variables. By making it possible to distinguish the impact on outcomes of one variable from the impacts of others, this analysis makes it possible to control for factors that may influence the results and obscure the effects the experiment is intended to identify.

opportunity cost—the value of alternatives not chosen, calculated as part of an analysis of the costs of the alternative that was chosen.

plug-in—estimates for particular costs that can be used to streamline cost analysis.

p-value—calculation of the probability that the data indicate a significant difference.

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 that the results can be compared across

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