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

■ Terms

absolute reliability. Indicates how much of a measured value, expressed in the original units, is likely to be due to error. (9,32)

absolute risk increase (ARI). The increase in risk associated with an intervention as compared to the risk without the intervention (or the control condition); the absolute difference between the control event rate (CER) and the experimental event rate (EER). (34)

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). (34)

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. (13)

active variable. An independent variable with levels that can be manipulated and assigned by the researcher. (14)

adjusted means. Means that have been adjusted based on the value of a covariate in an analysis of covariance. (30)

agreement. (see percent agreement)

allocation concealment. Implementation of a process of random assignment where those involved in the trial are shielded from knowing the upcoming participant group assignment. (14)

alpha coefficient. (see Cronbach’s alpha)

alpha (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. (23) (see also Cronbach’s alpha)

alternate forms reliability. Reliability of two equivalent forms of a measuring instrument. (32)

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. (18)

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. (23)

analysis of covariance (ANCOVA). Statistical procedure used to compare two or more conditions while controlling for the effect of one or more covariates. (15,30)

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. (25)

a priori comparisons. (see planned comparisons)

arm. (see treatment arm)

attributable risk. An estimate used to quantify the risk of disease in an exposed group that is attributable to the exposure, by removing the risk that would have occurred as a result of other causes (risk in the unexposed group). (34)

attribute variable. An ...

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