Single Subject

Jesus Valdez

Purpose

To study the changes in behavior of an individual exhibits after exposure to an intervention or treatment of some sort.

Essential characteristics

Line graphs Dependent outcome is expressed on y-axis Sequence of time is expressed on x- axis Involves extensive collection on subject Can be applied where group designs are

difficult

2 ways it differs from other forms of research

1. Baseline is followed by the independent variable

2. Figure caption near the bottom of the graph

What is and why baseline

What?

Graphic record of measurements taken prior to introducing an intervention in a time-series design

Why?

It’s the control before the treatment

The 6 Designs

A-B Reversal (A-B-A) A-B-A-B B-A-B A-B-C-B Multiple-baseline

A-B Design

Design in which measurements are repeatedly made until stability is presumably established (baseline), after which treatment is introduced and an appropriate number or measurements are made

A-B-A Design

Same as A-B design, except a second baseline is added

A-B-A-B Design

Same as A-B-A design, except a second treatment is added

B-A-B Design

Same as A-B-A-B design, except the initial baseline phase is omitted

A-B-C-A Design

Same as A-B-A design, except a second baseline phase is replaced by a modified treatment phase

Multiple-Baseline Design

Experimental design in which baseline data are collected on several behaviors for on subject, after which the treatment is applied sequentially over a period of time to each behavior

Threats to internal validity

Length of the baseline and conditions Number of variables changed form condition

to condition Degree and speed of change Return or not of baseline levels Number of baselines

Ways to control threat

Subject characteristics, mortality, testing, and history

Less effective with location, date collector characteristics

Weak in instrument decay, data collector bias, attitude

External validity

Are weak when it comes to generalizability Important to replicate to test generalization

Example of Single Subject

Onto the Internet