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Single-Subject Designs

Single-Subject Designs. There are two broadly defined approaches to experimental research group designs single-subject designs.

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Single-Subject Designs

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  1. Single-Subject Designs

  2. There are two broadly defined approaches to experimental researchgroup 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. 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 Summary Comparison of Group and Single-Subject Designs: Experimental Control

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

  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.

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