Single-Case Research Designs

1. 11 Single-Case Research Designs

2. Introduction • Single-case designs • use only one participant or one group of participants • no random assignment and no control group • single participant used most frequently • History of single-case designs • not case studies • research in psychology began with single case experiments • Pavlov, Ebbinghaus, Skinner • Fisher’s introduction of ANOVA • single-case designs became more acceptable with the growth in research in behavior therapy

3. Single-Case Designs • Time-series designs • with multiple data points before and after treatment is introduced • does not eliminate the history threat • assessment of a treatment effect is based on the assumption that the pattern of pretreatment responses would continue in the absence of the treatment • Simplest type of single-case design is ABA

4. ABA Design • Baseline (A) • the target behavior of the participant in its naturally occurring state or prior to presentation of the treatment condition • Treatment (B) • recordings of behavior after the treatment has been introduced • ABA • design in which the response to the treatment condition is compared to baseline responses recorded before and after treatment • baseline – treatment – baseline • demonstration of treatment effectiveness requires return to baseline • Reversal • change of behavior back to baseline level after withdrawal of treatment

5. ABA Example • Walker and Buckley (1968) • 9 year old exhibiting disruptive classroom behavior • baseline • % time child spent on academic assignments • baseline recorded until DV stabilized • treatment • points earned if no distraction occurred during a given time interval • points could be exchanged for model of his choice • return to baseline • when child had completed three successive ten-minute distraction-free sessions, the reinforcement of being able to earn points was withdrawn

6. ABA Designs • Problems with ABA design • ending on baseline not acceptable from therapist point of view because you are ending with a denial of treatment • solution – ABAB design may be used • some DVs may not revert to baseline when treatment is withdrawn due to carryover • solution – multiple-baseline design • withdrawal vs. reversal design • reversal design – design in which the treatment condition is applied to an alternative but incompatible behavior so that a reversal in behavior is produced

7. ABAB Design • Disruptive classroom behavior example • return to treatment condition after second baseline condition • should see a return of DV to treatment levels

8. Interaction Design • Tests the combined effects of two treatments • e.g., concrete and verbal reinforcement • Similar to factorial design in that you look at each treatment (IV) individually (main effects) and combined (interaction) • Must change only one treatment at a time • Must use both sequences to test the combined influence over the effect of just one variable

9. Interaction Design • Disadvantages • two participants may be required • interaction effect can be demonstrated only if each variable does not cause a maximum increment in performance

10. Multiple Baseline Design • Design in which the treatment condition is successively administered to several target participants, target outcomes (DVs), or target settings • alternative to ABA or ABAB when history threat may be suspected • no withdrawal or reversal involved • Design • baseline data collected on several participants, DVs, or settings • treatment successively administered to each target (i.e., staggered) • treatment effect demonstrated by a change in behavior only when treatment is given • Requires independence of behaviors to demonstrate an effect

11. Multiple Baseline Example • Van Houten, Van Houten, & Malenfant, 2007 • tested the effectiveness of a program designed to increase helmet use by middle school students when riding their bicycles • three schools were targeted, and baseline helmet use data were gathered at each school • the treatment program was introduced at one school at a time • increases in correct helmet use occurred when the helmet program was introduced in each school • when the campaign was introduced at the 2nd and 3rd schools, helmet use increased, but did not change at the schools still at baseline • this fingerprint or pattern of change provided evidence of the causal efficacy of the helmet advocacy program on helmet use by students

12. Changing-Criterion Design • Design in which a participant’s behavior is gradually shaped by changing the criterion for success during successive treatment periods • Design • baseline data taken on a single behavior • treatment introduced with a criterion level of performance that needs to be met • if criterion met, then 2nd criterion level set • target behavior increased with multiple criterion levels (at least two)

13. Changing-Criterion Design • Factors to consider in using this design • length of treatment • long enough for the behavior to stabilize • size of criterion change • large enough to notice a change • number of treatment phases • at least two, but enough to demonstrate a treatment effect

14. Changing-Criterion Design • Himadi, Osteen, Kaiser, & Daniel (1991) • study to reduce the delusional verbalizations of a 51-year-old white male with schizophrenia, chronic undifferentiated type • the investigators first obtained baseline data on the number of delusional answers given • the treatment session consisted of asking the patient a question that had reliably elicited a delusional answer and instructing the patient to respond to the question “so that other people would agree with your answers.” After the patient provided the appropriate answer, he was given a reinforcer consisting of a cup of coffee • Phase 1 criterion, the patient had to provide nondelusional responses to two questions • Phase 2, nondelusional responses to four delusion-eliciting questions

15. Methodological Considerations • Baseline • must be stable before treatment implemented • absence of trend or in the direction opposite of what is expected from the treatment • little variability • if variability in data, then track until stable or try to identify source of the instability • must also consider reactivity when tracking baseline data • Change only one variable at a time (Cardinal rule)

16. Methodological Considerations • Length of phases • no set rule – semblance of stability • possibility of extraneous variables creeping in with long phases • carry-over effect may require short phases • cyclic variations – maybe need to incorporate the cycle in all phases

17. Criteria for Evaluating Change • Experimental criterion • repeated demonstration of behavioral change should occur with treatment introduction • nonoverlap of treatment and baseline phases • Therapeutic criterion • clinical significance of a therapeutic or other psychological intervention for an individual or group of clients • researchers often use social validation – does it produce a change in the client’s daily functioning • social comparison – compare behavior with non-deviant peers • subject evaluation – do others who interact with the client see a change