A functional behaviour hypothesis is a concise, evidence-informed statement that explains the likely relationship between what happens before a behaviour, the behaviour itself, and what happens afterwards.
It is an important part of a Functional Behaviour Assessment (FBA) because it brings together information collected through interviews, observations, behaviour data and other relevant sources to develop an informed hypothesis about why a behaviour may be occurring and what function it may serve for the person.
A well-written functional behaviour hypothesis does more than describe the behaviour. It helps practitioners move from “What is happening?” to “What might this behaviour be communicating or achieving for this person?”
This guide explains how to formulate a functional behaviour hypothesis, what information to include, common mistakes to avoid, and how to write a hypothesis that can meaningfully inform Positive Behaviour Support.
What Is a Functional Behaviour Hypothesis?
A functional behaviour hypothesis, sometimes called a hypothesis statement or functional hypothesis, is a proposed explanation of the variables that appear to influence a behaviour of concern.
It is developed from the information gathered during the Functional Behaviour Assessment rather than from assumptions about the person.
- relevant setting events or contextual factors
- antecedents or triggers
- a clear description of the behaviour
- consequences or responses that follow the behaviour
- the likely function or purpose the behaviour serves for the person
The hypothesis is not a diagnosis and should not be presented as proven fact. It represents the best explanation supported by the evidence currently available.
As additional information and behaviour data become available, the hypothesis may need to be reviewed and refined.
Why Is a Functional Behaviour Hypothesis Important?
Behaviours that look similar can occur for very different reasons.
For example, two people may both leave a room when an activity begins. For one person, leaving may help them escape a task they find confusing or difficult. For another, the environment may be noisy and overwhelming. Another person may leave because doing so results in access to a preferred person or activity.
Simply describing the behaviour as “leaving the room” does not explain why it is occurring.
Understanding the likely function is important because Positive Behaviour Support strategies should address the person’s underlying needs and the variables contributing to the behaviour, rather than focusing only on stopping the behaviour.
What Are the Common Functions of Behaviour?
Functional Behaviour Assessment often considers whether behaviour may be associated with obtaining or accessing something, avoiding or escaping something, or meeting sensory, regulatory or other internally mediated needs.
- gaining social interaction, attention or connection
- accessing a preferred item, activity or experience
- escaping, avoiding, delaying or reducing a demand or activity
- communicating discomfort, distress or an unmet need
- increasing predictability or control
- regulating sensory input or emotional arousal
- meeting another individual need
These categories can be useful prompts for analysis, but practitioners should not select a function simply because it fits a predefined category. The proposed function should emerge from the available assessment evidence.
It is also possible for a behaviour to have more than one function, or for its function to differ depending on the situation.
Before Writing the Functional Behaviour Hypothesis
A functional hypothesis should come after information has been gathered and analysed, not before.
- interviews with the person and people who know them well
- ABC (Antecedent–Behaviour–Consequence) data
- direct observations
- behaviour frequency, duration or intensity data
- communication information
- health and medical information where relevant
- sensory and environmental factors
- routines and activities
- quality-of-life factors
- previous assessments and reports
- information about what happens before, during and after the behaviour
The purpose is to identify patterns across the available evidence. A single incident may suggest a possibility, but it will not necessarily provide enough evidence to confidently identify a behavioural function.
How to Write a Functional Behaviour Hypothesis
Step 1: Clearly Define the Behaviour
Start with an observable and measurable description of the behaviour.
Avoid vague or interpretive labels such as aggressive, challenging, defiant, manipulative, attention-seeking or non-compliant.
Rather than: “Sam becomes aggressive.”
Consider: “Sam hits others with an open or closed hand, pushes others away and may throw objects within reach.”
The description should allow different people observing the behaviour to recognise when it has and has not occurred.
Step 2: Identify Relevant Setting Events
Setting events are broader circumstances that may alter the likelihood of behaviour occurring. Examples might include poor sleep, illness or pain, changes to routine, significant life events, fatigue, hunger, previous stressful events, changes in familiar support people, or prolonged exposure to demanding or overwhelming environments.
A setting event does not necessarily trigger the behaviour immediately. Instead, it may make the person more vulnerable to particular triggers or demands later.
Only include setting events when there is evidence that they are relevant to the individual.
Step 3: Identify Antecedents and Triggers
Next, examine what tends to happen immediately before the behaviour.
- being asked to begin or stop an activity
- being told that something is unavailable
- an unexpected change
- waiting
- a difficult task
- another person approaching
- increased noise or activity
- loss of access to something preferred
- communication breakdown
- transitions between activities
Look for patterns rather than isolated events. Ask: What tends to be happening immediately before the behaviour occurs?
Step 4: Examine What Happens After the Behaviour
Consider what typically happens following the behaviour. Does a task stop, delay or change? Does someone provide reassurance or interaction? Does the person gain access to something? Does another person move away? Does the environment become quieter? Is the person able to leave the situation? Is a difficult interaction brought to an end?
Consequences are important because they can help identify what the behaviour may achieve or change for the person. However, what happens after a behaviour does not automatically prove its function. It needs to be interpreted alongside the wider assessment evidence.
Step 5: Identify the Most Plausible Function
Bring the information together and ask: What does the behaviour appear to help the person obtain, avoid, communicate, regulate or change?
The answer should be supported by identifiable patterns in the evidence.
For example, repeated observations might show that a particular behaviour occurs following difficult demands, is less likely during preferred or appropriately supported activities, and is frequently followed by the demand being delayed or removed. This pattern may support a hypothesis that the behaviour functions, at least in part, to escape or delay difficult demands.
The wording should reflect the strength of the available evidence. Where evidence is limited, language such as “may,” “appears to,” “is possibly associated with” or “the available information suggests” is more appropriate than presenting the function as established fact.
Step 6: Write the Functional Hypothesis Statement
Once the patterns have been identified, bring them together into a concise statement.
When [relevant context/setting event] and [antecedent] occur, the person is more likely to [observable behaviour], which appears to result in or support [likely function/outcome].
This is a framework rather than a rigid formula. The final hypothesis should reflect the complexity of the person’s actual circumstances.
Functional Behaviour Hypothesis Example
Consider the following fictional example.
Assessment information
Jordan sometimes pushes materials from the table, shouts “no” and leaves the work area.
Across several observations, this behaviour is more likely when Jordan is asked to complete unfamiliar written tasks, particularly when instructions contain several steps.
The behaviour is less likely when tasks are broken into smaller steps and when Jordan can ask for help or a break.
Following the behaviour, the written task is often paused while an adult assists Jordan or allows time away from the activity.
Possible functional hypothesis
When Jordan is presented with unfamiliar or multi-step written tasks, particularly when already tired or overwhelmed, Jordan may push materials away, shout “no” and leave the work area. The available information suggests that these behaviours may function to communicate difficulty and obtain a pause from, or assistance with, tasks that Jordan experiences as demanding.
Notice that this statement identifies the context, antecedent, behaviour and likely function, while using appropriately cautious language. It does not describe Jordan as difficult, oppositional or manipulative.
Another Functional Behaviour Hypothesis Example
Consider a person who frequently calls out repeatedly to support staff.
Assessment information indicates that this occurs most often during long periods without interaction and decreases when regular opportunities for meaningful social engagement are available.
During extended periods with limited social interaction, Alex is more likely to repeatedly call out to nearby support staff. Staff typically approach and interact with Alex following the behaviour. Across the available observations, this pattern suggests that calling out may function, at least in part, to initiate social connection and interaction.
Again, the hypothesis explains a relationship between context, behaviour and outcome rather than attaching a negative label to the person.
Can a Behaviour Have More Than One Function?
Yes. Human behaviour is complex, and the same behaviour can serve different functions in different circumstances.
For example, a person may shout during a difficult task to communicate that they need it to stop, in a busy environment because they are overwhelmed, and at another time to gain someone’s attention.
If the evidence indicates different patterns, these should not be forced into a single explanation. The functional hypothesis may need to describe multiple plausible functions or different context-dependent pathways.
What If There Is Not Enough Evidence to Identify the Function?
Sometimes an FBA does not provide enough evidence to confidently determine why a behaviour is occurring. This should be stated clearly.
The available information suggests a possible relationship between the behaviour and difficult task demands; however, the evidence is currently limited and does not support a confident conclusion regarding function.
This is preferable to inventing a function simply because an FBA template requires one. A hypothesis can be refined as additional observations and information become available.
Association Is Not the Same as Causation
One of the most important principles when interpreting behaviour data is that a repeated association does not necessarily demonstrate causation.
For example, if a behaviour frequently occurs when a particular support worker is present, it would be inappropriate to conclude automatically that the support worker causes the behaviour. Other variables may explain the pattern, such as the activities usually completed during that shift, the time of day, communication style, transitions, environmental demands or differences in routine.
Functional assessment requires practitioners to examine competing explanations rather than jumping to the most obvious conclusion.
Common Mistakes When Writing a Functional Behaviour Hypothesis
1. Restating the behaviour instead of explaining its function
Weak: “Jordan engages in challenging behaviour when given difficult work.” This describes a relationship but does not explain what the behaviour may achieve.
2. Treating assumptions as facts
Weak: “Jordan behaves this way because he wants to avoid work.” Unless there is strong supporting evidence, this wording is too definitive.
3. Using judgemental language
Terms such as “manipulative,” “attention-seeking,” “naughty,” “defiant” or “controlling” can obscure the person’s underlying needs. Describe observable behaviour and analyse its context instead.
4. Assuming attention is the function whenever someone responds
People naturally respond when behaviour occurs. The fact that attention follows a behaviour does not by itself demonstrate that obtaining attention is its function.
5. Ignoring communication
Behaviour may communicate pain, confusion, distress, sensory overload, a desire to stop, a need for assistance, or difficulty expressing something through the person’s available communication system.
6. Ignoring health and wellbeing
A behavioural explanation should not replace consideration of possible health, medical, pain, sleep or wellbeing factors.
7. Forcing behaviour into one function
Where evidence supports multiple explanations, document them. The purpose of an FBA is to understand the person – not to make the evidence fit a predetermined category.
From Functional Hypothesis to Positive Behaviour Support
Writing the hypothesis is not the end of the Functional Behaviour Assessment process. Its real value is in informing Positive Behaviour Support (PBS).
- address unmet needs
- modify relevant environmental factors
- improve predictability and accessibility
- support communication
- reduce unnecessary or overwhelming demands
- teach meaningful alternative skills
- increase choice and autonomy
- support emotional and sensory regulation
- strengthen quality of life
- provide safe and consistent responses when behaviour occurs
Strategies should logically relate to the functional assessment. For example, if behaviour appears to communicate that a task is too difficult, simply teaching the person to tolerate increasingly difficult tasks may fail to address the underlying problem. Support might instead involve examining task demands, communication options, environmental accommodations, choice, assistance and meaningful ways to request a break.
These strategies typically form part of the person’s Behaviour Support Plan.
Functional Behaviour Hypothesis Template
When: [Describe relevant setting events, context and/or antecedents.]
The person is more likely to: [Describe the behaviour in observable terms.]
This is commonly followed by: [Describe relevant consequences or changes in the environment.]
The available evidence suggests: [State the most plausible function or functions and the level of confidence supported by the evidence.]
Example
When: presented with unfamiliar multi-step tasks, particularly when tired,
Jordan is more likely to: push materials away, shout “no” and leave the work area.
This is commonly followed by: the task being paused and Jordan receiving assistance or time away.
The available evidence suggests: these behaviours may function to communicate difficulty and obtain assistance with, or a temporary break from, tasks experienced as demanding.
Develop Your Functional Behaviour Hypothesis in the Behaviour Help App
If you are completing a Functional Behaviour Assessment, the Behaviour Help App provides a structured online FBA template that guides practitioners through gathering and organising assessment information, analysing behavioural patterns and developing an evidence-informed functional behaviour hypothesis.
Rather than working across separate Word documents, forms and spreadsheets, assessment information can be brought together within the FBA process to support development of the functional hypothesis and the broader Positive Behaviour Support process.
Once the FBA is completed, it can be generated and downloaded as a professional Word or PDF FBA report.
Frequently Asked Questions
What is a functional hypothesis in an FBA?
A functional hypothesis is an evidence-informed explanation of the circumstances associated with a behaviour and the likely function or purpose the behaviour serves for the person.
What should a functional behaviour hypothesis include?
It will commonly include relevant setting events or context, antecedents, an observable description of the behaviour, relevant consequences and the most plausible function supported by the available evidence.
Is a functional behaviour hypothesis the same as an ABC analysis?
No. ABC data records Antecedents, Behaviour and Consequences surrounding behavioural events. These observations can contribute evidence to an FBA. A functional hypothesis integrates patterns from ABC data with other relevant assessment information to propose why the behaviour may be occurring.
Is a functional hypothesis a fact?
No. It is a hypothesis based on the best available evidence. Its wording should reflect the quality and consistency of that evidence, and it should be reviewed when new information becomes available.
Can there be more than one behavioural function?
Yes. A behaviour may have multiple functions, and its function may differ across contexts.
What if the function of behaviour is unclear?
Practitioners should document the uncertainty rather than assign an unsupported function. Further assessment and observation may help clarify the hypothesis.
How do you write a functional behaviour hypothesis?
Define the behaviour clearly, examine relevant setting events and antecedents, analyse what typically follows the behaviour, identify patterns across the available evidence, consider alternative explanations and formulate the most plausible function using language that reflects the strength of the evidence.
Key Takeaway
A strong functional behaviour hypothesis does not simply label a behaviour or guess why it occurs. It brings together evidence to describe when the behaviour is more likely to occur, what happens, what tends to follow, and what the behaviour may achieve or communicate for the person.
The strongest hypotheses remain person-centred, evidence-informed and open to revision. Most importantly, understanding function should lead to better support – not simply better descriptions of behaviour.