Chapter 13Chapter 13

Single-Subject Single-Subject DesignsDesigns

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Topics

1. Types of Single-Subject Designs2. Case Study Designs3. Experimental Single-Subject Designs4. Alternative Types of Single-Subject Research

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Types of Single-Subject Designs

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Types of Single-Subject Designs

• Two purposes– Descriptive

• Single-subject naturalistic observation• Single variable is observed after the application of a

particular treatment

– Experimental• Reversal design • Multiple-baseline design

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Types of Single-Subject Designs (cont’d.)

• Descriptive and experimental intents may be combined

• In 1895, a 9-year-old boy swallowed some scalding hot clam chowder– Describe a person’s behaviors or psychological

processes– Scientifically model these behaviors or cognitive

processes– Can be used to direct experimental procedures

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Case Study Designs

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Naturalistic Case Studies

• Case study– Based on the logic of describing, analyzing,

interpreting, and evaluating a set of events and relationships within a framework or theory (Bromley, 1986)

• Typical descriptive case study: focuses on either problematic or exceptional behaviors

• Advantage: ability to describe processes not easily reduced to a single variable

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Naturalistic Case Studies (cont’d.)

• Examples: – Case study of Anna O.– Morton Prince’s The Dissociation of a Personality

(1913)– Oliver Sacks’s Awakenings (1973)– Ramachandran (1998) summarized his work on

phantom limb pain– Maslow (1970) studied exceptional people whom

he considered to be self-actualizing

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One-Shot Case Studies

• Narrative that summarizes an experimenter’s direct observations of a participant’s behavior after some sort of treatment has been performed

Figure 13.1 One-shot case study design. In the figure, X represents the treatment given to a single subject; O refers to the experimenter’s observations

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One-Shot Case Studies (cont’d.)

• May be used to study the effects of an event that took place in the past

• Example: – A male patient (H.M.) underwent bilateral

temporal lobe surgery in 1953– As a result of the surgery, this man had no

memory of the present– From the case study, information has been

obtained about memory

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One-Shot Case Studies (cont’d.)

• As an experimental design– The case study does not give us the ability to make

strong inferences• Kazdin (2003b, 2010): the single-subject design

is misnamed and misunderstood• The single-subject design “should not be

demeaned by identification with the one-group posttest-only design” (Cook & Campbell, 1979, p. 96)

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Experimental Single-Subject Designs

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Experimental Single-Subject Designs

• Determine the manner in which one variable influences another

• Time series approach– Establish a series of measurements over time– Series of measurements forms a basis of

comparison with another series of measurements after the independent variable is introduced

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Experimental Single-Subject Designs (cont’d.)

• Establishing a baseline – Serves as a reference point – Gives us some sense of how stable or labile the

dependent variable is when the independent variable is not present

• Intrasubject replication: pattern is repeated within a single participant

• Intersubject replication: pattern is repeated between participants

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Reversal Design

• Common type of single-subject design • Term reversal: comes from the shifting of the

baseline and treatment conditions• May use any number of reversals• ABA design: design that measures a

participant’s behavior before, during, and after a treatment

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Reversal Design (cont’d.)

Figure 13.2 This figure represents an ABAB single-subject reversal design. X represents the administration of the independent variable; O represents the behavioral observations made on the subject. Note that O1 and O3 represent the observations of the dependent variable in the absence of the treatment condition, and O2 and O4 represent the observations of the dependent variable in the presence of the treatment condition

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Figure 13.3 This figure represents an alternative method of diagramming an ABAB single-subject reversal design. Depending on the dependent variable, the change from baseline to treatment may be seen either as an increase (e.g., percentage of intervals with correct behavior) or as a decrease (e.g., percentage of intervals with problem behavior)

Source: Dyer, Dunlap, and Winterling (1990).

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Figure 13.4 Results of an ABA study of three students

Source: Dyer, Dunlap, and Winterling (1990).

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Reversal Design (cont’d.)

• Limitation: – Will work only when we are studying the effect of

treatment conditions on behaviors that return quickly to baseline levels once the treatment is over

• Use a multiple-baseline design– When studying the long-lasting effects of various

independent variables on single participants

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Multiple-Baseline Design

• Monitor several behaviors of a single subject simultaneously

• Once baseline levels are established for each behavior– Apply treatment to one of these behaviors

• Once the first behavioral shift is noted– Treatment is applied to the next behavior, and so

on

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Multiple-Baseline Design (cont’d.)

Figure 13.5 Multiple-baseline design. In this design, several behaviors (A, B, C, and D) are monitored simultaneously. The treatment is applied successively to each of these behaviors. The continuation of baseline measures after treatment sometimes is omitted. Note that evidence suggestive of a causal relationship would consist of a successive shift in baseline activity as each successive behavior receives the treatment condition

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Figure 13.6 Multiple-baseline design. This type of representation is an alternative to the one presented in Figure 13.5. In this case the baseline measures were not continued after the treatment condition was introduced. The letters A, B, C, and D could represent either different behaviors of a given participant, the same behavior of one participant in different situations, or the same behavior of different participants.

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Multiple-Baseline Design (cont’d.)

• Keep in mind: each behavior being monitored must be independent of the others

• Limited value in studying inappropriate classroom behaviors

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Multielement Design

• Compare different levels of a given variable or different treatments

• Also called the alternating treatment design or simultaneous treatment design

• Key element: incorporates many reversals

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Multielement Design (cont’d.)

• Advantages: – Examine the changes within the context of

background variables that are difficult to change– Any differences in the effects of different

treatments seem to emerge quickly• Limitation: best suited to changes that are

short-lived

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Making Sense of Single-Subject Experimental Results

• How do you know that the particular pattern of results is meaningful? – Logic– Replication

• Traditional experimental single-subject designs do not offer a cutoff level – Researcher must determine the meaning of the

pattern observed

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Alternative Types of Single-Subject Research

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Alternative Types of Single-Subject Research

• Recent trends:– Use inferential procedures in single-subject

studies (Gorman & Allison, 1998)– Use single-subject approaches conceptually as an

aid in describing theoretical cognitive models

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Summary

• Naturalistic case study: traditional means of describing an individual

• Experimental single-subject designs: use a series of measurements over time to establish stability

• Types of experimental single-subject designs: reversal design, the multiple-baseline design, and the multielement design