An Overview of Experimental Design

1. An Overview of Experimental Design

2. Experimental Control Definition • Is a predictable change in behavior (dependent variable) that can be reliably produced by the systematic manipulation of some variable (independent variable)

3. Goal of Behavior Analysis • Experimentally determine the effects of environmental manipulation on behavior • and demonstrate the effects can be reliably produced

4. Internal Validity • The extent to which an experiment shows that changes in behavior are a function of the independent variable • and not the result of uncontrolled or unknown variables

5. Problem: Confounding Variables • Variables known or suspected to exert an uncontrolled influence on the dependent variable • Effects must be evaluated and eliminated to demonstrate experimental control • Problem: • May not know all of the confounding variables • Time of day • Barometric pressure • Other unknown

6. Solution • Eliminate as many uncontrolled variables as possible OR • Hold constant the influence of all other variables except the independent variable

7. Behavior • Can be an individual phenomenon • Can be a continuous phenomenon • Assumes That: • Behavior is determined • Behavioral variability is extrinsic to the organism

8. Behavior as an Individual Phenomenon • Examine a person’s interaction with the environment • With ABA • Strategy often based on within-subject (single-subject) designs

9. Contrast: Dynamic / Continuous Behavior • Behavior changes over time • Requires continuous measurement over time • Complete record of behavior as it occurs in context • Often uses cumulative recorder types of methodologies for recording • Systematic repeated measurement is the “hallmark” of ABA

10. Assumes • The occurrence of any event is determined by the functional relations it holds to other events • Behavior is a natural phenomenon • Behavioral variability is the result of some environmental influence • In ABA • Try to find out what it is • Try to find interventions to change the behavior

11. Components of Experiments in ABA • Examine at least one • Subject or participant • Behavior (dependent variable) • Setting • Treatment or intervention condition (independent variable)

12. Research Question(s) • Are statements about what the person wants to learn about a behavior by conducting an experiment. • Specifically: What are the effects of the independent variable on the dependent variable • Are always written down: • Nothing exists until it is on paper (Brigham) • Allows you to identify what you are examining • Allows you to identify problems • Allows you to create solutions

13. Many Different Designs • Group Designs • Single Subject • Multiple Baseline • Simultaneous Treatment • Others • Each has its advantages and disadvantages. • Past research and experience helps you decide on the type of design to use

14. Experiment using Groups • Randomly selected pool of subjects from relevant population • Divided into experimental and control groups • Pretest, application of independent variable to experimental group, and posttest

15. Problem • Group data may not be representative of individual performance • Some individuals within a group may stay the same or decrease, while the improvement of others could make it appear as overall average improvement • To be most useful, treatment must be understood at an individual level • Individual can mean a group in an organization

16. Group Data Masks Variability • Hides variability that occurs within and between subjects • Use statistical control to compensate • Should not be a substitute for experimental control • To control effects of any variable, must either hold it constant or manipulate it as an independent variable

17. ABA • Often uses single-subject designs • Subject becomes its own control • Measures of the subject’s behavior during each phase of the study • Allows you to compare variables as they are presented or withdrawn during various conditions

18. May have Single or Multiple Dependent Variables • Single • Only manipulation one variable • Can often see clear results • Multiple • Still manipulate one variable • Have multiple dependent variables

19. Reasons • Gives data patterns that can serve as controls when evaluating & replicating the effects of an independent variable • Allows you to assess the presence or extent an independent variable may effect behaviors other than the response class. • Allows you to determine whether changes in behavior of others occur during the course of an experiment • Changes may explain changes in the subject’s behavior

20. Measurement Systems and Visual Analysis • Observation & recording procedures must be conducted in a standardized manner • Standardization involves every aspect of the measurement system • Definition of the target behavior to scheduling of observations • Behavior analysts must develop skills in the detection of changes in the level, trend, and degree of variability in behavioral data

21. Independent and Dependent Variables • Independent Variable • The aspect of the environment that the experimenter manipulates • The researcher controls or manipulates this variable independent of the subject’s behavior or any other event • Dependent Variable • The behavior that changes as a result of changes in the independent variable • Is the thing you are observing

22. Experimental design • Nonparametric study • Independent variable is either presented or absent during a time period or phase of the study • Parametric study • The value of the independent variable is manipulated • Seeks to discover the differential effects of a range of values

23. Fundamental Rule in Experimental Designs • Change only one variable at a time • Experimenter can attribute any measured changes to a specific independent variable • If investigating the effects of a “treatment package” • Ensure that the entire package is presented or withdrawn each time a manipulation occurs • Allows you to make causal statements

24. Some Additional Rules • Do not get locked into textbook “designs” • Select & combine experimental tactics that best fit the research questions

25. Steady State Strategies • Repeated exposure of a given subject to a given condition • Try to eliminate or control extraneous influences on behavior & obtaining a stable pattern of responding before introducing the next condition

26. Baseline Data in ABA • Serves as a control condition • Does not imply the absence of intervention • Absence of a specific independent variable • Why examine? • Allows you to observe a level of responding in the absence of an independent variable • Allows you to make comparisons when you introduce an intervention

27. Benefits • You can obtain descriptions of antecedent-behavior-consequent correlations for the planning of an effective treatment • Valuable guidance in setting initial criteria for reinforcement • Baseline data may reveal the behavior targeted for change does not warrant intervention

28. Types of Baseline Data Patterns • Stable baseline (A) • Ascending baseline (B and C) • Variable baseline (D)

29. Types of Baseline Data Patterns

30. Example

31. Problem • May be due to other variables

32. Need Verification • Done by termination or withdrawal of the treatment variable

33. Verification

34. Can use Replication

35. Conclusions • Lots of aspects to experimental designs • Need to make sure you know the strengths and weaknesses of the designs you plan to use. • Want to ensure your conclusions are based on solid data.