Single-Subject Designs

There are two broadly defined approaches to experimental research

group designs single-subject designs

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

Single-subject designs are also called:

Time series functional analysis within-subject experimental analysis of behavior single-case experimental designs

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

Components of Single-Subject Designs Single-subject designs are typically

depicted by using letters A and BA = the baseline and withdrawal phases

B = treatment phase there are different single-subject

designs– some are descriptive– some are experimental

Descriptive Designs

A = baseline only (diary study) B = treatment only (case study) AB = baseline + treatment (case study;

no control)

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

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

Components of Single-Subject Designs specify the problem select the design measure the problem repeated measures baseline analysis of data

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

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

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.

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

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

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

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

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

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

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

Comparison of Single-Subject and Group Designs In group designs, power is

demonstrated through statistical significance

Summary Comparison of Group and Single-Subject Designs: Experimental ControlGroup 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: Power/SignificanceGroup Designs Statistical significance

Single-Subject Designs

Replication– across phases within

subjects– across subjects

Visual inference of graphed data– slope, trend, level

Visual Analysis of Single-Subject Designs Group designs determine the

effectiveness/significance at predetermined probability levels, e.g., .05 or .01

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

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

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

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

Criteria for Evaluating Single-Subject DesignsDetermine 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

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

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

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

Advantages of Single-Subject Designs Provide clinicians with a tool for

demonstrating accountability to their clients, administrators, and funding sources.

Disadvantage of Single-Subject Designs Reluctance to generalize results from

single subjects to groups of individuals

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

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.