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Single Subject Research and Evidence-based Interventions: Are SSDs Really the Ugly Stepchild?. Ronnie Detrich Randy Keyworth Jack States Wing Institute. The Problem. Standards of evidence are necessary to identify evidence-based interventions.

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single subject research and evidence based interventions are ssds really the ugly stepchild

Single Subject Research and Evidence-based Interventions: Are SSDs Really the Ugly Stepchild?

Ronnie Detrich

Randy Keyworth

Jack States

Wing Institute

the problem
The Problem
  • Standards of evidence are necessary to identify evidence-based interventions.
    • Allow us to evaluate the strength of evidence across studies for a particular intervention.
  • Single subject designs have not always been accepted as a legitimate means for demonstrating the impact of an intervention.
    • What Works Clearinghouse has no standards for single subject designs.
the problem3
The Problem
  • In many sub-disciplines within education and psychology single subject designs have been primary method for identifying effective interventions.
    • Developmental disabilities
    • Autism
    • Severe behavior problems
  • If single subject designs are not accorded scientific status then many effective interventions will not be validated as evidence-based interventions.
characteristics of single subject design
Characteristics of Single Subject Design
  • The purpose of SSDs is to demonstrate a functional relation between an independent and dependent variable.
    • Intense analysis of a few subjects demonstrates the functional relation.
  • Reliance on visual inspection good for identifying variables that have “whopping” effect.
    • Identifies socially significant effects.
  • Well designed studies control for threats to internal validity.
    • Internal validity: the degree to which alternative explanations for the obtained effects have been controlled for through the experimental design.
characteristics of single subject design5
Characteristics of Single Subject Design
  • Demonstrates the robustness or generality of an independent variable through direct and systematic replication.
    • Direct replication: exposing the same or different subjects to exactly the same experimental arrangement that resulted in identifying a functional variable.
      • Reversal designs both within and across subjects
      • Multiple baselines across subjects
    • Systematic replication: varying some features of the original experimental arrangement.
      • Different subject characteristics, different settings, different responses, different “doses” of the functional variable.
generality and external validity
Generality and External Validity
  • Generality and External Validity are related but distinct concerns.
    • Generality describes the boundary conditions of a functional relation.
      • Under what conditions does the functional relation “break down”?
    • External validity refers to degree to which the results of a research study can be extended to other populations, settings, and conditions.
      • Degree of external validity is always contextual. Depends on the similarity between research and intervention conditions.
      • Answers actuarial questions that concern program administrators and policy makers- “how big a bang will I get and what is the probability of impact”?
generality and external validity7
Generality and External Validity
  • Single subject designs are most often criticized because of issues related to external validity.
    • In large part behavior analysts have not given much consideration to subject characteristics.
    • Behavior analysts have been more concerned with establishing the robustness of a few variables (reinforcement, stimulus control).
      • Body of knowledge is established through direct and systematic replication.
      • As we move from the study of single variables and basic behavioral processes to multi-component packages the distinction between generality and external validity becomes more confused.
benefits of single subject design
Benefits of Single Subject Design
  • A rigorous methodology for identifying functional variables.
  • Allows scientist to see pattern of action of the variable of interest:
    • Can make informed statements about:
      • Acquisition
      • Maintenance
      • Generalization
benefits of single subject design9
Benefits of Single Subject Design
  • It is possible to study low incidence populations and behaviors.
  • Cost-Effective relative to group designs.
    • Can evaluate intervention before subjecting to large scale studies.
  • Close continuous contact with the data allow for great flexibility.
  • Research can be completed by scientist-practitioner in practice settings.
    • Can easily test clinical hypothesis.
    • Best method for progress monitoring in applied settings.
limitations of single subject design
Limitations of Single Subject Design
  • Does not answer “actuarial” questions related to external validity very well.
    • Was not intended to answer those questions.
  • Reliance on visual inspection may result in unreliable interpretation.
    • There are no established standards for visually evaluating data.
      • Several researchers have criticized relying on visual inspection as means of interpretation. (DeProspero & Cohen,1979) because of relatively low agreement between observers.
limitations of single subject design11
Limitations of Single Subject Design
  • Methods for aggregating results across studies have not been established.
    • Meta-analysis approaches may be useful.
      • This is very important for validating interventions as evidence-based.
      • Practitioners and decision-makers do not have time nor access to all of the primary source data.
  • Standards for validating interventions as evidence-based with SSDs are just emerging.
    • No consensus among these standards.
are ssds the ugly stepchild
Are SSDs the Ugly Stepchild?
  • Should not be
    • As long as they are used to identify functional variables.
  • But not everyone agrees:
    • Some excellent texts on group designs poorly describe SSDs.
  • We have work to do.
recommendations
Recommendations
  • Develop appropriate meta-analysis methods for single subject research.
  • Develop standards for visual inspection.
    • Complex, very politically sensitive task.
  • Work with national organizations such as What Works Clearinghouse to assure that single subject research given equal status to group designs.