1. Single-Subject Designs

2. There are two broadly defined approaches to experimental research group designs single-subject designs

3. Both approaches apply the components of the scientific method to their approach to research - the difference between group and single-subject designs lies in the manner in which the principles of the scientific method are put into operation in designing studies

4. Single-subject designs are also called:
Time series
functional analysis
within-subject
experimental analysis of behavior
single-case experimental designs

5. Single-Subject Designs
Use this design to demonstrate a functional relationship between changes in the IV and the resultant changes in the DV
it provides an empirical verification that behavior change occurred because intervention occurred and no other cause

6. Components of Single-Subject Designs
Single-subject designs are typically depicted by using letters A and B
A = the baseline and withdrawal phases
B = treatment phase
there are different single-subject designs
some are descriptive
some are experimental

7. Descriptive Designs A = baseline only (diary study)
B = treatment only (case study)
AB = baseline + treatment (case study; no control)

8. Experimental Single-Subject Designs
Withdrawal Designs
ABA
BAB
ABAB TREATMENT -
Reversal Designs NO TREATMENT
ABA COMPARISONS
ABAB
Multiple Baseline Designs
MB x Behaviors
MB x Subjects
MB x Settings

9. Experimental Single-Subject Designs
Interaction Designs
Reduction (A - BC - B - C)
Addition (A - B - C- BC)
use these designs to look at interactive effects of individual components of tx
Component assessment designs
Alternating Treatments Designs B
A - C - B or C or D D
Treatment-Treatment Comparison

10. Components of Single-Subject Designs
specify the problem
select the design
measure the problem
repeated measures
baseline
analysis of data

11. Specify the problem
Identify the behavior that needs to be changed or treated
the behavior must be specified as clearly as possible in order for it to be reliably measured

12. Select the design
There are a variety of SS designs that are defined by different phases
select design on basis of question want to answer
Withdrawal, Reversal or MB designs answer question “Is treatment effective?”
Interaction designs answer question, “What are the interactive components of treatment?”
ATD answer question, “Which treatment is more effective?”
Phases in SS designs consist basically of a baseline (or no tx phase) and tx phases.
These phases can be combined in different ways to derive different designs

13. Measure the problem
After the behavior has been clearly defined, the clinician decides how the behavior will be measured,e.g., correct/incorrect responses, rate of response, length of response, etc.

14. Repeated Measures
The behavior is repeatedly measured before, during, and after treatment to determine if any changes have occurred in that behavior.
This component is the HALLMARK of single-subject designs

15. Baseline
Before treatment is initiated, the behavior is measured over a period of time (1-2 weeks, few days)
the BL provides a comparison of “before” and “after” treatment in order to evaluate the effectiveness of the treatment approach

16. Analysis of data
Single-subject designs rely on visual analysis of the graphed data rather than on statistical analysis of the data to make decisions about the significance of the treatment approach
slope, trend, and level of graphed data

17. Comparison of Single-Subject and Group Designs
Group designs and SS designs share similar attitudes and components, but they use the components differently
in SS designs, as in all experimental research, variables are manipulated and then you measure the effect of the IV on the DV
SS designs differ from group designs in how they demonstrate experimental control

18. Comparison of Single-Subject and Group Designs
Experimental control in SS designs is demonstrated in 2 ways:
in SS designs, the SUBJECT serves as their own control and is administered all conditions of the experimental condition and then all conditions are re-measured
therefore, don’t need a control group to demonstrate experimental control
control behavior or control phase

19. Comparison of Single-Subject and Group Designs
Group designs demonstrate experimental control in 3 ways:
two groups (control group and experimental group)
random selection of subjects from a larger population of subjects
statistical tests
help to look beyond the variability found in examining the individual performances of the subjects within each group.
Thus, idiosyncratic behavioral patterns are ignored by pooling subjects’ data and the statistic serves as a control for extraneous variables

20. Comparison of Single-Subject and Group Designs
Single-subject designs also differ from group designs in terms of how power/significance of the results is determined
In SS designs, power/significance is demonstrated in 2 ways:
through the replication of tx effectiveness across AB phases within a subject and/or replication of tx effectiveness across subjects
through the trend, slope, and level of the visually presented data

21. Comparison of Single-Subject and Group Designs
In group designs, power is demonstrated through statistical significance

22. Summary Comparison of Group and Single-Subject Designs: Experimental Control
Group Designs
Control + Experimental Groups
Random selection of subjects
Statistical tests
Single-Subject Designs
Each subject serves as OWN control
Control behavior or control phase

23. Summary Comparison of Group and Single-Subject Designs: Power/Significance
Group Designs
Statistical significance
Single-Subject Designs
Replication
across phases within subjects
across subjects
Visual inference of graphed data
slope, trend, level

24. Visual Analysis of Single-Subject Designs
Group designs determine the effectiveness/significance at predetermined probability levels, e.g., .05 or .01

25. Visual Analysis of Single-Subject Designs
Single-subject designs determine the effectiveness of the IV generally by visual examination of the graphed data
therefore the reader of SS research must be cautious in interpreting tx effectiveness from visual inference
3 parameters important to visually presented data and graphs
trend
slope
level

26. Trend
The effectiveness of the IV is measured by comparing the direction of the behavior before tx and after tx is administered
3 directions the behavior may take:
increase in the occurrence of the behavior
decrease in the occurrence of the behavior
no change in occurrence of the behavior
to be believable, the behavior must be measured a sufficient number of times to establish that it is not change before tx (min. of 3x recommended) and there must be a stable BL

27. Slope
The degree of slope in the trend will indicate how strong the trend is.
A pronounced slope is stronger evidence that the behavior is changing than if the slope is a gentle one

28. Level
The level at which the behavior is occurring before treatment is important in determining the significance of the change in the behavior following tx

29. Criteria for Evaluating Single-Subject Designs
Determine if:
the data are reliable
the behavior was altered when intervention was administered (level)
the change observed was significant (slope)
the results are generalizable to other individuals
the BL was stable (trend)
there was no variability within phases and/or phases

30. Advantages of Single-Subject Designs
Hard to find large N of subjects for group designs
don’t need a large N of allegedly homogeneous subjects with a particular communication disorder, random selection of Ss for sample and random assignment to groups
ethical question to withhold tx for control group
SS designs are clinically based - don’t need to have a group of CD individuals who will not receive tx in order to have a control group

31. Advantages of Single-Subject Designs
Get detailed information on individual subjects rather than pre-post scores
you get individual data points across time and therefore can detect individual differences in response to tx
easier to control for Ss since each Ss serves as his/her own control
SS designs are “intervention designs” that can be used for exploring tx effectiveness which is a primary issue in CDIS

32. Advantages of Single-Subject Designs
SS designs are “practice based” and “practitioner oriented” in that they are flexible and changes can be made during the course of tx if deemed necessary by the clinician
Researcher-clinician gap is narrowed
environment for conducting SS research
can easily be incorporated into clinical practice without disruption
conducted in clinic during clinic hours and regularly scheduled tx sessions

33. Advantages of Single-Subject Designs
Provide clinicians with a tool for demonstrating accountability to their clients, administrators, and funding sources.

34. Disadvantage of Single-Subject Designs
Reluctance to generalize results from single subjects to groups of individuals

35. Considerations in Using Single-Subject Designs
Length of phases
should be equal (each tx phase)
however, this is not always possible
therefore, usually use criterion levels and maximum number of sessions
Counterbalancing
whenever more than one behavior is treated sequentially, there is risk of order effects
order effects can be controlled in MB studies by counterbalancing
this requires a second subject who goes through study in an opposite training order from 1st Ss
therefore, more than 1 Ss needed for MB studies

36. Considerations in Using Single-Subject Designs
Selecting Behaviors
2 behaviors selected for tx in a MB study must be different (independent) enough that they must not impact each other
PRINCIPLE: 2 different behaviors and a single tx
Baseline
BL measures must be obtained on all DV responses
the BL period must be sufficient enough to determine the stability of the response
the BL must demonstrate a trend, slope, and level that is sufficiently different from the DV when the IV is applied.