PSYB01 - Chapter 11 notes.doc

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Anna Nagy

Chapter 11 Single Case, Quasi-Experimental, and Developmental Research In chapter 8 we looked at classic experimental designed in which participants are assigned to experimental controls and a variable is manipulated This process has high internal validity This chapter will look at 3 types of special research circumstances The first is an instance in which the effect of an independent variable must be inferred from an experiment with only one participants a single case study The second we will describe pre-experimental and quasi-experimental designs that may be considered if it is not possible to use true experimental designs Third, we will look at research designs that study changes that occur over age Single Case Experimental Designs Single case experimental designs have traditionally been called single-subject designs but are now called single case designs (Barlow and Hersen, Shadish, Cook, and Cample) and single participant (Morgan and Morgan) Early interest in single case designs in psychology came from B.F. Skinners work with reinforcement Today research using single participant design is often seen in clinical, counselling, educational, and other applied settings Developed from the need to see if experimental manipulation had had an effect on a single participant In a single case design, the subjects behaviour is measured over time during a baseline control period. The manipulation is then introduced during a treatment period and the participants behaviour is continued to be observed A change in behaviour from the baseline to the treatment periods is evidence for effective manipulation The problem is there are many explanation for the change (alternative examples) because another event may have coincided with the treatment introduction, therefore the following single-case designed address this problem Reversal Designs The basic issue in a single case experiment is how to determine that the manipulation of the independent variable had an effect One way is to demonstrate the reversibility of the manipulation A simple reversal design takes the following form: A (baseline period)B (treatment period)A (baseline period) This is also know as the ABA design and requires behaviour observation during the baseline control (A), during the treatment (B), and during a second baseline (A) Sometimes called a withdrawal design If behaviour changed when the treatment is introduced then reversed when the treatment is removed, it is evidence for effectiveness of the treatment Some treatments do not produce an immediate effect, but the single case design can be appropriate for these as long as they maintain a long treatment period The ABA design can be greatly improved by extending it to ABAB or even to ABABAB this is done to address two problems of the ABA design: 1. a single reversal is not extremely powerful evidence for the effectiveness of treatment observed results may have been due to a random fluctuation in behaviour or the treatment may have coincided with some other event. These possibilities are much less likely is they treatment has been shown to have an effect 2 or more times 2. the second problem is ethical. Barlow and Hersen point out that is does not seem ethical to end the experiment with withdrawal of treatment when the treatment could be very beneficial to the participant (therefore use ABAB and end with treatment) a control group may also be used in a reversal design Multiple Baseline Designs the reversal of some behaviours is unethical or impossible (eg is it unethical to reverse treatments that reduce dangerous behaviour or a treatment may provide a long-lasting effect that is not reversible) in such cases multiple measures over time can be made before and after the manipulation if the manipulation is effective, a change in behaviour will be immediately observed and the change will continue to be reflected in other behaviors in a multiple baseline design the effectiveness of the treatment is demonstrated when a behaviour changes only after the manipulation is introduced and the change must be viewed under multiple circumstances to rule out the possibility that other events were responsible there are several variations of the multiple baseline design. in the multiple baseline across subjects, the behaviour of several subjects is measured over time; for each subject, the manipulation is introduced at a different point in time. Eg. Figure 11.2 on page 207 there was a change in behaviour following manipulation, and since the manipulation was introduced at different times, we can rule out explanations based on chance, historical events, etc in a multiple baseline across behaviors several different behaviors of a single individual are measured over time; at different times, the same manipulation is applied to all behaviors. For example, an award system can be implemented to increase grooming, socializing, and reading in mental patients. if each behaviour improved when the manipulation was introduced, there is evidence of its effectiveness. the third variation is multiple baseline across situations where the same behaviour is measured in different settings (eg home and work). The manipulation isintroduced at a different time in each setting and if the change occurs in each situation only after the manipulation is introduced it is evidence that it is effective Replications in Single Case the procedures can be replicated for other cases, therefore enhancing the generalizability of the results usually reports of research using single case experimental design presents the results from several subjects in several settings the tradition in single case research has been to present the results from each subject individually rather than group the data because grouping the data can provide a misleading picture of individual responses single case experiments can be especially useful for someone who is applying some change technique in a natural environment eg a teacher trying a new technique in the classroom also beneficial because complex statistical analysis is not required Program Evaluation researchers often investigate applied research questions and conduct evaluation research may use true experimental designs, surveys, observational techniques, etc Quasi-Experimental Designs address the need to study the effect of an independent variable in settings in which the control features of true experimental designs cannot be achieved. A quasi-experimen
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