CH 11

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University of Toronto Scarborough
Anna Nagy

CHAPTER 11: SINGLE CASE, QUASI-EXPERIMENTAL, AND DEVELOPMENTAL RESEARCH This chapter focuses on three types of special research situations 1. The instance in which the effect of an independent variable must be inferred from an experiment with only one participant- single case experimental designs. 2. Describing pre-experimental and quasi-experimental designs that may be considered if it is not possible to use one of the true experimental designs described in chapter 8 3. Considering research designs for studying changes that occur with age. SINGLE CASE EXPERIMENTAL DESIGNS DEFINITION: An experiment in which the effect of the independent variable is assessed using data from a single participant. Single case experimental designs have traditionally been called single-subject designs, but now the terms used are single case and single participant. EARLIER INTEREST: In psychology came from research on reinforcement schedules pioneered by B.F Skinner TODAY: Research using single case designs are often seen in clinical, counseling, educational, and other applied settings. Were developed from a need to determine whether an experimental manipulation had an effect on a single research participant. HOW THE SINGLE CASE EXPERIMENT IS MEASURED? o Subjects behavior is measured over time during a baseline control period. Baseline: in a single case design, the subjects behavior during a control period before introduction of the experimental manipulation. o The manipulation is then introduced during a treatment period, and the subjects behavior from baseline to treatment periods is evidence for the effectiveness for manipulation. o PROBLEM: There could be many explanations for the change other than the experimental treatment (i.e., alternative explanations) Example: some other event may have coincided with the introduction of the treatment. www.notesolution.comREVERSAL DESIGNS DEFINITION: a single case design in which the treatment is introduced after a baseline period and then withdrawn during a second baseline period. It may be extended by adding a second introduction of the treatment. Sometimes called a withdrawal design. The basic issue in single case experiments is how to determine that the manipulation of the independent variable had an effect. o One method is to demonstrate the reversibility of the manipulation o REVERSAL DESIGN takes the following form, A (baseline period) B (treatment period) A (baseline period) This design is called an ABA A behavior be observed during the baseline control period and again during the treatment B behavior be observed during the period and also during a second baseline A - behavior be observed during period after the experimental treatment has been removed. Sometimes this is called a withdrawal design, in recognition of the fact that the treatment is removed or withdrawn. EXAMPLE: The effect of a reinforcement procedure on a childs academic performance could be assessed with an ABA design. The number of correct homework problems could be measured each day during the baseline(A) A reinforcement treatment procedure would then be introduced in which the child received stars for correct problems; the stars could be accumulated and exchanged for toys and candy. (B) Later, this treatment would be discontinued during the second baseline period (A)
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