Intensity and Interresponse Time Measurement

Summary: This page explains intensity and interresponse time (IRT) measurement in ABA. Intensity measures the magnitude or force of a behavior, while IRT measures the time between consecutive instances of a behavior. You’ll learn when to use each measurement type, implementation methods, and practical applications in both skill acquisition and behavior reduction programs.

Intensity and interresponse time (IRT) are specialized measurement dimensions in Applied Behavior Analysis (ABA). These measurement approaches provide important information about the magnitude of behaviors and the timing between consecutive responses.

What is Intensity Measurement?

Intensity measurement involves recording the magnitude or force of a behavior.

Key Characteristics of Intensity Measurement

Definition: The strength, magnitude, or force of a behavior
Data recorded: Level or degree of behavior on a defined scale
Example notation: “Level 3 intensity” or “85 decibels”
Appropriate for: Behaviors with varying degrees of force or magnitude
Advantages: Captures severity beyond simple occurrence
Limitations: Often requires specialized equipment or subjective judgment

When to Use Intensity Measurement

Intensity measurement is most appropriate when:

The force or magnitude of the behavior is clinically significant
The behavior occurs at varying levels of intensity
Intervention goals target reducing the severity of behavior
Other dimensions (frequency, duration) don’t capture the behavior’s impact
The behavior can be measured on a defined scale or with specialized equipment

Examples of Behaviors Measured by Intensity

Volume of vocal behavior (measured in decibels)
Force of aggressive behaviors
Pressure applied during self-injury
Magnitude of property destruction
Severity of pain (using pain scales)
Degree of emotional response
Intensity of physical exercise

Implementing Intensity Measurement

To implement intensity measurement:

Define intensity levels with clear, observable criteria
Create a rating scale or select appropriate measurement equipment
Train observers to consistently rate or measure intensity
Record intensity for each occurrence of the behavior
Calculate summary measures if needed (e.g., average intensity)
Assess reliability between observers

Types of Intensity Scales

Several approaches can be used to measure intensity:

Objective measurement: Using equipment like decibel meters or pressure sensors
Likert-type scales: Rating behavior on a numeric scale (e.g., 1-5)
Descriptive scales: Using defined categories (e.g., mild, moderate, severe)
Visual analog scales: Marking intensity on a continuous line
Permanent product measures: Measuring physical evidence left by the behavior

What is Interresponse Time (IRT) Measurement?

Interresponse time (IRT) measurement involves recording the time between consecutive instances of a behavior.

Key Characteristics of IRT Measurement

Definition: Time elapsed between the end of one response and the beginning of the next
Data recorded: Length of time (seconds, minutes)
Example notation: “45 seconds IRT” or “2.3 minutes between responses”
Appropriate for: Analyzing response patterns and behavioral rhythms
Advantages: Reveals temporal patterns not captured by other measures
Limitations: Requires precise timing and continuous observation

When to Use IRT Measurement

IRT measurement is most appropriate when:

The timing between responses is clinically significant
The goal is to increase or decrease time between behaviors
The behavior occurs repeatedly with varying intervals
Response patterns or behavioral rhythms are being analyzed
Rate-based interventions are being implemented

Examples of Behaviors Measured by IRT

Time between instances of self-injurious behavior
Interval between requests for attention
Time between instances of hand-raising in class
Spacing between vocal stereotypy episodes
Time between mands (requests)
Interval between aggressive outbursts
Time between reinforcer deliveries

Implementing IRT Measurement

To implement IRT measurement:

Define the behavior with clear start and end criteria
Select a timing method (e.g., stopwatch, timer app, video recording)
Start timing when one instance of the behavior ends
Stop timing when the next instance begins
Record each IRT in consistent units (typically seconds)
Calculate summary measures if needed (e.g., average IRT)

Comparing Intensity and IRT

Aspect	Intensity	Interresponse Time
Definition	Magnitude or force of behavior	Time between consecutive responses
What is measured	Strength or severity	Temporal spacing
Measurement approach	Rating scales or equipment	Timing devices
Clinical focus	Behavior severity	Response patterns
Example	Level 4 aggression on 5-point scale	30 seconds between self-injury instances
Goal examples	Decrease intensity of tantrums	Increase time between requests for attention

Practical Applications

Skill Acquisition

In skill acquisition programs, intensity and IRT measurements help track:

Response quality: Measuring intensity of appropriate behaviors
Fluency: Decreasing IRT between responses in a sequence
Independence: Increasing IRT between prompts and responses
Effort: Measuring intensity of participation
Pacing: Optimizing IRT for learning activities

Behavior Reduction

For behavior reduction programs, these measurements help monitor:

Behavior severity: Tracking changes in intensity of problem behaviors
Response patterns: Analyzing IRT to identify antecedents
Intervention effects: Measuring changes in intensity or IRT
Extinction bursts: Monitoring intensity during intervention
Recovery rate: Tracking IRT following challenging episodes

Data Collection Methods

Intensity Measurement Methods

Methods for measuring intensity include:

Rating scales: Numeric or descriptive scales for severity
Specialized equipment: Devices that measure force, volume, etc.
Permanent product analysis: Measuring physical evidence of behavior
Physiological measures: Heart rate, skin conductance, etc.
Structured observation tools: Standardized assessment protocols

IRT Measurement Methods

Methods for measuring IRT include:

Stopwatches: Manual timing between responses
Event recording software: Programs that calculate time between recorded events
Video analysis: Recording sessions for precise timing
Automated sensors: Devices that detect and time behaviors
Data collection apps: Mobile applications with IRT calculation features

Graphing Intensity and IRT Data

Intensity Graphs

When graphing intensity data:

Y-axis: Intensity level or measurement
X-axis: Observation sessions or days
Data points: Recorded intensity for each occurrence
Summary points: Average intensity per session
Phase lines: Vertical lines indicating intervention changes
Trend lines: Lines showing direction of intensity change

IRT Graphs

When graphing IRT data:

Y-axis: Time between responses (seconds, minutes)
X-axis: Response number or session
Data points: Each recorded IRT
Cumulative graphs: Showing total responses over time
Scatterplots: Revealing patterns in response timing
Trend lines: Indicating changes in response spacing

Common Errors in Intensity and IRT Measurement

Intensity Measurement Errors

Common errors in intensity measurement include:

Subjective bias: Personal judgment affecting ratings
Scale drift: Changing criteria for intensity levels over time
Inconsistent definitions: Unclear criteria for different intensity levels
Equipment issues: Improper use or calibration of measurement devices
Context effects: Environmental factors affecting intensity measurement
Observer reactivity: Behavior changing when being measured

IRT Measurement Errors

Common errors in IRT measurement include:

Timing inaccuracies: Delays in starting or stopping timing
Missed responses: Failing to observe all instances of the behavior
Inconsistent response definitions: Unclear when responses begin or end
Equipment failures: Timer malfunctions or user errors
Calculation errors: Mistakes in computing time between responses
Confusing IRT with other measures: Mixing up IRT with duration or latency

Practice Examples

Example 1: Aggressive Behavior

Scenario: A behavior analyst is implementing an intervention to reduce the intensity of aggressive behaviors.

Measurement approach:

Behavior: Physical aggression
Method: 5-point intensity scale (1=mild, 5=severe)
Data:
- Baseline: avg. intensity 4.2
- Intervention week 1: avg. intensity 3.8
- Intervention week 2: avg. intensity 3.1
- Intervention week 3: avg. intensity 2.3
Analysis: Decreasing trend in aggression intensity
Next steps: Continue intervention based on positive results

Example 2: Self-Injurious Behavior

Scenario: A clinician is tracking changes in the pattern of self-injurious behavior.

Measurement approach:

Behavior: Head hitting
Method: IRT recording between instances
Data:
- Baseline: avg. IRT 45 seconds
- Intervention week 1: avg. IRT 90 seconds
- Intervention week 2: avg. IRT 180 seconds
- Intervention week 3: avg. IRT 300 seconds
Analysis: Increasing trend in time between self-injury instances
Next steps: Continue intervention and begin teaching replacement behaviors

Example 3: Vocal Stereotypy

Scenario: A teacher is measuring both the intensity and pattern of vocal stereotypy.

Measurement approach:

Behavior: Vocal stereotypy
Methods:
- Intensity: Decibel level using sound meter
- Pattern: IRT between episodes
Data:
- Intensity: Decreased from avg. 85dB to 72dB
- IRT: Increased from avg. 2 minutes to 8 minutes between episodes
Analysis: Improvements in both dimensions
Next steps: Implement generalization strategies across settings

Key Points to Remember

Intensity measures the magnitude or force of a behavior
Interresponse time (IRT) measures the time between consecutive instances of a behavior
Intensity measurement often requires rating scales or specialized equipment
IRT measurement requires precise timing and clear response definitions
Both measures can provide valuable information not captured by frequency or duration alone
Intensity is particularly useful for behaviors where severity is a concern
IRT is valuable for understanding response patterns and behavioral rhythms
Graphing these dimensions helps visualize changes in behavior quality and timing
Consistent operational definitions are essential for reliable measurement
Regular assessment of interobserver agreement ensures measurement accuracy