| Mixed design | An experimental design that includes between-subjects as well as within-subjects factors. Also called a split-plot design.
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| Nested Design | An experimental design with a within-subjects factor in which different levels of one independent variable are included under each level of a between-subjects factor.
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| Covariate | A correlational variable (usually a characteristic of the subject) included in an experiment to help reduce the error variance in statistical tests.
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| Quasi-independent variable | A variable resembling the independent variable in an experiment, but whose levels are not assigned to subjects at random (the subject’s age, for example).
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| Quasi-experimental design | A design resembling an experimental design but using quasi-independent rather than true independent variables.
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| Time series design | A research design in which behavior of subjects in naturally occurring groups is measured periodically both before and after introduction of a treatment.
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| Interrupted time series design | A variation of the time series design in which changes in behavior are charted as a function of time before and after some naturally occurring event.
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| Equivalent time samples design | A variation of the time design in which a treatment is administered repeatedly, with each administration followed by an observation period.
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| Nonequivalent control group design | A time series design in which levels of the independent variable are represented by different categories rather than differing amounts.
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| Pretest—posttest design | A research design that involves measuring a dependent variable (pretest), the introducing the treatment, and then measuring the dependent variable a second time (posttest).
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| Solomon four-group design | An expansion of the pretest-posttest design that includes control groups to evaluate the effects of administering a pretest on your experimental treatment.
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| Cross-sectional design | A developmental design in which participants from two or more age groups are measured at about the same time. Comparisons are made across age groups to investigate age-related changes in behavior.
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| Longitudinal design | A developmental design in which a single group of subjects is followed over a specified period of time and measured at regular intervals.
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| Cohort-sequential design | A developmental design including cross-sectional and longitudinal components.
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