Small N Designs

Small N Designs

Single Subject Research Design (SSRD) involves studying a single individual or system by taking repeated measurements of 1 or more dependent variables and systematically applying & sometimes, withdrawing or varying the independent variable.

Small N Designs

• Designs that involve a very small number of participants

• Rather than reporting measures of central tendency, focus is placed on observations of individual scores/behaviors

Practical Reasons for doing Small N Research

• Procedures are costly / time consuming

• Procedures are invasive

• Procedures require intensive training

• Participants are rare / hard to find

Single-Subject Designs

• Goal: Behavior of a single participant must be shown to change as a result of the treatment

• Three Components

1) Target behavior must be operationally defined

2) Baseline level of responding must be established

3) Conduct treatment and monitor behavior 

• A-B Designs (baseline → treatment)

• Withdrawal Designs

– A-B-A Design

– A-B-A-B Design

Flood et al. (2002)

Study of ADHD Treatment Efficacy

• Participants: 3 10-year olds previously diagnosed with ADHD, not on meds

• IV: Treatment (single level)

– Ss paired with non-ADHD peer who praises Ss for “on task” behavior and prompts Ss after “off task” behavior

• DV: “Off task” behavior

– Looking away from assigned task for 3 seconds

Multiple Baseline Design

• Three varieties of Multiple Baseline Designs

• Baselines are established for:

(1) 1 type of behavior in 2+ individuals in 1 setting

(2) 2+ types of behaviors in 1 individual in 1 setting

(3) 1 behavior in 1 individual across 2+ settings

Wagaman et al. (1993)

• Multiple Baselines Across Subjects

– (1) 1 behavior in 2+ individuals in 1 setting 

• Participants: 8 school children

• IV: “Regulated breathing” treatment

• DV: Stuttering

Criticisms of Small N Designs

• Low external validity

• How do we handle this criticism?

– Evaluate generalizabilty within the design

– Replicate and extend the study 

Ethical Considerations

• Withdrawing a treatment that has changed behavior for the good

• Treatments can be controversial

• Case of special needs children

– Benefits of treatment