Glossary Items Starting with "A"

a posteriori comparison: See post hoc comparison.
a priori comparison: See planned comparison.
ABA design: See reversal design.
abscissa: The x-axis on a graph.
abstract: A brief description of a research study that appears at the beginning of the paper and is included in abstract journals, such as Psychological Abstracts.
abstract number system: The commonly used number system with its well-defined rules and characteristics, including identity, magnitude, equal intervals, and true zero.
accessible population: That subset of a target population that is available to the researcher and from which the sample is drawn.
ad hoc sample: Sample of participants drawn from an accessible population. Characteristics of the ad hoc sample must be described to define the limits of generalizability.
all-or-none bias: The tendency to see statements as either true or false when they are actually probabilistic. Virtually all scientific theories are probabilistic in that they correctly predict what will happen a percentage of the time.
alpha level: Level of Type I error (the probability of rejecting the null hypothesis when the null hypotheses is true).
Analysis of Covariance (ANCOVA): Statistical procedure similar to analysis of variance, used to evaluate whether two or more groups have different population means. Analysis of covariance statistically removes the effects of extraneous variables on the dependent variable and hence increases the power of the statistical test.
analysis of variance (ANOVA): Statistical procedure used to analyze for mean differences between two or more groups. ANOVAs compare the variability between groups with the variability within groups. Many variations of analysis of variance are possible, including repeated measures ANOVAs and factorial ANOVAs.
ANOVA summary table: Table that organizes the results of an analysis of variance computation. For each source of variation, the appropriate degrees of freedom, sums of squares, mean squares, and F-ratios are listed. (Examples are given in Chapters 10 to 12.)
apparatus subsection: That section of a research report in which physical aspects of the study (apparatus, measuring instruments, etc.) are described.
applied psychology: Any use of psychological principles, theories, or technologies to deal with existing problems or concerns. Applied psychology refers to research that is specifically aimed at understanding and correcting problems faced by people.
applied research: Research to provide solutions to practical problems. Applied research is contrasted with basic research.
archival records: Any source of data (such as census data) for events that have already occurred.
artifact: Any apparent effect of a major conceptual variable that is actually the result of an uncontrolled confounding variable. Artifacts threaten the validity of research.
artificial intelligence: Machines that are designed to evaluate and respond to situations. Most artificial intelligence machines are computer-based, and many of them have achieved remarkable levels of performance in specific areas.
assent: Agreeing to participate when one is unable to give legal consent.
association: Relationship or correlation.
assumptions (of science): Basic tenets that form the basis for more complex scientific theory and research.
attrition: Potential confounding variable in research. Attrition is the loss of participants before or during the research. The participants who remain may not be representative of the population. Hence, conclusions drawn may not generalize to the entire population.
authority: A way of acquiring knowledge. New ideas are accepted as valid because some respected authority has declared the idea to be true.
automation: Use of equipment to conduct most or all aspects of presenting stimuli and recording participants' responses. Automation reduces the work, increases precision in data gathering, and minimizes experimenter bias.
average deviation: The sum of the deviations from the mean divided by the number of scores.