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

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

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

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)

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)

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)

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

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

agreement. (See percent agreement.)

alpha coefficient. (See Cronbach's alpha.)

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)

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

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

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)

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)

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)

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)

a priori comparisons. (See planned comparisons.)

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

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

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