1. 11
Single-Case Research Designs

2. Introduction Single-case designs History of 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) Treatment (B) ABA Reversal
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had completed three successive ten-minute distraction-free sessions, the reinforcement of being able to earn points was withdrawn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some DVs may not revert to baseline when treatment is withdrawn due to carryover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