Single-Case andSmall Sample Research

Chapter 14

Exceptions to Research Findings Behavioral science is probabilistic.

There are always exceptions to any particular finding

Research findings uncover generalities and trends.

Exceptions do not invalidate research findings, but should they be ignored?

Different Approaches

Nomothetic approach – aims to establish general principles and broad generalizations that apply across individuals

Idiographic approach – aims to describe, analyze, and explain the behavior of individuals

Two Types of Single-Case Studies

Single-case experimental designs

Case studies

Single-Case Experimental Designs

Unit of analysis is not the experimental group, as it is in group designs, but rather the individual participant

More than one participant may be studied, but their responses are analyzed individually

Cannot analyze these data with inferential statistics such as t-tests and F-tests

Criticisms of Group Designs and Analyses

(1) Error Variance

Group design argument Averaging across participants provides a more

accurate estimate of a variable’s general effect Group designs allow us to estimate the amount of

error variance in our data

BUT, group averages can be misleading!

Example: Learning Curves

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Result of Averaging Across Participants

An Individual Participant

Criticisms of Group Designs and Analyses

Single-case argument Error variance is partly created by averaging over

participants in a group design (interparticipant variance)

Researchers using group designs ignore the “real” error variance within the participant

This intraparticipant variance is important to understand.

Criticisms of Group Designs and Analyses

(2) Generalizability Group design argument – averaging the

scores of several participants reduces the idiosyncratic responses of any one participant to show the general effect

Single-case argument – averaging responses may not accurately describe any particular participant’s responses

Criticisms of Group Designs and Analyses

(3) Reliability Group design argument – reliability of

findings is established by replicating studies

Single-case argument – reliability of findings should be established via: Intraparticipant replication – replicating the

effects of the independent variable with a single participant

Interparticipant replication – seeing whether the effects obtained for one participant generalize to other participants in the same study

Single Participant Designs

ABA Designs

ABA Design Behavior is measured (Baseline period; A) Independent variable is introduced (B) Behavior is measured (A)

Can also replicate within an individual (ABABAB….)

Example of an ABAB Single-Case Design

Fisher, Thompson, Hagopian, Bowman, & Krug (2000)

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Baseline BaselineTreatment Treatment

Effects of a treatment (“functional communication training with extinction”) on a 19-year old male with autism and profound mental retardation

Multiple-I Designs Multiple-I designs – single-case

experimental designs that present varying nonzero levels of the independent variable ABC (DEFG…) Design

A - Baseline B - One level of the independent variable C - Another level of the independent variable

ABACA design – inserts a baseline period between each introduction of a level of the independent variable

Multiple Baseline Designs

Two or more behaviors studied simultaneously Obtain baseline on all behaviors Introduce an independent variable that is

predicted to affect only one behavior Allows the researcher to show that the

independent variable is causing the target behavior to change and is not affecting the other behaviors

Data from Single-Participant Designs

Results are typically shown in graphs Graphic analysis – researcher visually

inspects the graph of the data for an individual participant to see if the independent variable had an effect

Criticized for having not having explicit criteria for deciding when an effect is significant

Uses of Single-Case Experimental Designs

Operant conditioning; schedules of reinforcement and punishment

Psychophysiological processes; effects of drugs

Behavior modification – techniques for changing problem behaviors based on operant conditioning

Critique of Single-Participant Designs Effects are not necessarily generalizable

Individual participants may not be representative of the population

Neglect of interactions among variables Ethical issues

Example: Do you withdraw an effective treatment from a particularly troubled client in a reversal design?

Case Study Research Case study – a detailed study of a single

individual, group, or event May use information from numerous sources:

observation, interviews, questionnaires, news reports, and archival records

All information is compiled into a narrative description

Example: Phineas Gage

Uses of the Case Study Method Source of Insight and Ideas

Describe rare phenomena

Psychobiography – applying concepts and theories from psychology in an effort to understand famous people

Illustrative anecdotes (e.g.: George Vaillant)

A Case Study of Hitler"The drama and tragedy of Hitler's life are

the projection onto the world of his own inner conflicts and his attempts to solve them. The split in Hitler's personality seems clearly to be due to his identification both with is mother, whom he passionately loved, and with his father, whom he hated and feared... The inner conflict is projected into the world where Germany comes to represent the mother, and the Jew and--for a time--the Austrian State, the father." (Vernon, 1942)

Limitations of the Case Study Approach

Failure to control extraneous variables Alternative explanations can not be ruled out

Observer biases All observations may be conducted by a single

researcher No way of determining reliability and validity of

these observations