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Numbers in parentheses indicate the chapter in which the term is introduced.

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A-B design. A single-case design with two phases: A represents the baseline phase, and B represents the intervention phase. (12)

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A-B-A design. A single-case withdrawal design in which a second baseline phase is introduced. (12)

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absolute risk increase (ARI). The increase in risk associated with an intervention as compared to risk without the intervention (or control condition); the absolute difference between the control event rate (CER) and the experimental event rate (EER). (28)

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absolute risk reduction (ARR). The reduction in risk associated with an intervention as compared to the risk without the intervention (or the control condition); the absolute difference between the experimental event rate (EER) and the control event rate (CER). (28)

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accessible population. The actual population of subjects available to be chosen for a study. This group is usually a nonrandom subset of the target population. (8)

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active variable. An independent variable with levels that can be manipulated and assigned by the researcher. (9)

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adjusted means. Means that have been adjusted based on the value of a covariate in an analysis of covariance. (24)

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agreement. (See percent agreement.)

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alpha coefficient. (See Cronbach's alpha.)

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alpha level (α). Level of statistical significance, or risk of Type I error; maximum probability level that can be achieved in a statistical test to reject the null hypothesis. Symbols α1 and α2 are used to denote level of significance for one- and two-tailed tests, respectively. (18)

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alphanumeric data. In data processing, the entry of values that contain symbols or letters. (30)

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alternate forms reliability. Reliability of two equivalent forms of a measuring instrument. (5, 26)

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alternating treatment design. A single-case design in which two (or more) treatments are compared by alternating them within a session (or in alternate sessions). (12)

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alternative hypothesis (H1). Hypothesis stating the expected relationship between independent and dependent variables; considered the negation of the null hypothesis. The alternative hypothesis is accepted when the null hypothesis is rejected. (18)

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analysis of covariance (ANCOVA). Statistical procedure used to compare two or more treatment groups while controlling for the effect of one or more confounding variables (called covariates). (24)

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analysis of variance (ANOVA). Statistical procedure appropriate for comparison of three or more treatment groups or conditions, or the simultaneous manipulation of two or more independent variables; based on the F statistic. (20)

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a priori comparisons. (See planned comparisons.)

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area probability sample. A form of cluster sampling in which geographic areas serve as the units of analysis. (8)

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ARIMA (autoregressive integrated moving average). Statistical technique for analysis of data from time-series studies. ...

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