Statistical infrequency | AQA A-Level Psychology Revision
Updated: Sep 9
For 7182 specification, first teach in September 2025
AQA A-Level Psychology | Free Revision Notes
Estimated study time: 40 minutes
These Statistical infrequency A-Level Psychology revision notes explain how behaviour or characteristics may be defined as unusual when they occur rarely within a population. Statistical infrequency offers a numerical and apparently objective way to identify possible mental health difficulties, but rarity alone does not always indicate a problem. Exceptionally high intelligence is unusual but desirable, while some recognised disorders are relatively common. This lesson begins the four AQA definitions used in the field of mental health.
Learning Objectives 🎯
By the end of this revision page, you should be able to:
Define statistical infrequency.
Explain how a frequency distribution can be used to identify unusual characteristics.
Apply statistical infrequency to examples of behaviour.
Distinguish statistical rarity from psychological harm.
Evaluate the usefulness and limitations of statistical infrequency.
Compare statistical infrequency with other definitions in the field of mental health.
Revision Notes 📚
Statistical infrequency A-Level Psychology revision overview
Statistical infrequency defines a behaviour or characteristic as unusual when it is rare or uncommon within a population.
Researchers first collect information about a large group of people.
They can then examine:
The most common scores or behaviours.
The average score.
How widely scores vary.
How many people fall at each extreme.
Whether an individual’s score is unusually far from the average.
A characteristic found in only a small proportion of the population may be described as statistically infrequent.
The basic idea is:
The less frequently a behaviour or characteristic occurs, the more statistically unusual it is.
However, statistical unusualness does not automatically mean that a person has a mental health difficulty.
What does statistically infrequent mean?
Infrequent means occurring rarely.
A statistically infrequent characteristic may be one that:
Very few people display.
Produces a score far from the population average.
Appears at one of the extreme ends of a distribution.
Is uncommon when compared with an appropriate reference group.
Examples might include:
An exceptionally low intelligence quotient.
An exceptionally high intelligence quotient.
A very unusual emotional response.
A behaviour shown by only a small proportion of the population.
The definition focuses on frequency, not on whether the characteristic is:
Harmful.
Distressing.
Unwanted.
Socially acceptable.
Helpful to the person.
This distinction is central to evaluating the definition.
Frequency distributions
What is a distribution?
A distribution shows how scores or characteristics are spread across a population.
Suppose psychologists measure a characteristic in a large sample.
They might record:
The score obtained by each person.
How many people obtained each score.
Where most scores are concentrated.
Which scores are rare.
The results can be displayed using:
A frequency table.
A histogram.
A frequency curve.
A graph showing the shape of the distribution.
Understanding normal and skewed patterns of scores helps explain how psychologists identify statistically unusual results.
The normal distribution
A normal distribution is a symmetrical, bell-shaped distribution.
In a normal distribution:
Most scores cluster around the centre.
Scores become less common as they move away from the centre.
Very high scores are rare.
Very low scores are rare.
The two sides of the distribution are approximately symmetrical.
The central score is represented by the mean, which is covered further in calculating and interpreting averages.
The extremes of a distribution
The extreme ends are sometimes called the tails of the distribution.
Scores in these areas are statistically unusual because relatively few people obtain them.
A simple diagram would look like this:
Very low and rare ← Most people near the average → Very high and rare
Statistical infrequency identifies people at either extreme as different from most of the population.
This creates an immediate problem:
Very low scores may sometimes indicate difficulty.
Very high scores may be valuable or desirable.
Both are rare, but they do not necessarily have the same psychological meaning.
Variability in a distribution
Two populations could have the same average but differ in how widely their scores are spread.
Psychologists can examine this spread using measures such as:
The range.
Standard deviation.
A standard deviation indicates how much scores typically differ from the mean.
A smaller standard deviation means scores are more tightly grouped.
A larger standard deviation means scores are more spread out.
The calculation and interpretation of this measure are developed through range and standard deviation.
Statistical cut-off points
To use statistical infrequency, psychologists must decide where ordinary variation ends and unusual variation begins.
This requires a cut-off point.
A cut-off point is the score beyond which a characteristic is considered sufficiently rare to require attention.
For example, a psychologist might decide that scores at the extreme lower end of a cognitive assessment are statistically unusual.
However, deciding where to place the cut-off involves judgement.
There is no natural line in a distribution clearly labelled:
“Normal on this side and abnormal on the other.”
A person just beyond a cut-off may be very similar to someone just within it.
This makes the boundary partly subjective, even though the scores themselves are numerical.
Applying statistical infrequency to intelligence
Intelligence quotient
An intelligence quotient, or IQ, is a score obtained from a standardised assessment of intellectual abilities.
IQ scores are compared with scores from an appropriate population.
Most people obtain scores near the average.
Very low and very high scores occur less frequently.
Low IQ as an example
An extremely low IQ score is statistically infrequent.
Such a score can contribute to the identification of intellectual disability.
Statistical infrequency is useful here because it provides:
A standardised measurement.
A comparison with the wider population.
A way of identifying people who may need further assessment.
A basis for arranging appropriate educational or practical support.
Official AQA mark-scheme guidance identifies an extremely low IQ score at the lower end of a normal distribution as an appropriate example of statistical infrequency.
High IQ as a counterexample
An extremely high IQ score is also statistically infrequent.
However, high intelligence is not normally considered evidence of poor mental health.
It may be:
Valued.
Useful.
Associated with academic strengths.
Beneficial in some situations.
This demonstrates that:
Statistical rarity is not sufficient to define psychological difficulty.
The definition may identify unusualness, but it does not tell us whether that unusualness is harmful.
Comparing the two extremes
Characteristic | Statistically infrequent? | Usually viewed as a mental health difficulty? |
Exceptionally low IQ | Yes | It may contribute to identification of intellectual disability |
Exceptionally high IQ | Yes | No |
Average IQ | No | No conclusion can be drawn from frequency alone |
This is one of the strongest limitations of statistical infrequency.
Applying the definition to behaviour
A step-by-step method
When applying statistical infrequency, ask:
What behaviour or characteristic is being measured?
What is typical within the relevant population?
How frequently does the behaviour occur?
Is the person’s score near the centre or at an extreme?
Does rarity alone justify identifying a mental health difficulty?
Would another definition provide useful additional information?
Example 1: an unusual fear
A person experiences an intense fear of a highly unusual object.
If very few people share this response, the fear is statistically infrequent.
However, frequency alone does not tell us:
Whether the person is distressed.
Whether the fear affects everyday life.
Whether the person avoids important activities.
Whether treatment is needed.
To answer those questions, psychologists might also consider the ability to manage ordinary life.
Example 2: rare talent
A student can remember an exceptionally long sequence of numbers after hearing it once.
This ability may be statistically infrequent.
However, it is not necessarily evidence of a mental health problem.
It may be a useful and highly valued ability.
Example 3: an uncommon habit
A person follows a daily routine that very few other people follow.
The behaviour is statistically infrequent.
However, unless the habit causes distress, danger or serious disruption, its rarity may have little clinical importance.
Example 4: persistent low mood
A person experiences persistent low mood and loss of interest.
If many people experience similar symptoms, the behaviour may not be extremely statistically rare.
However, it may still form part of a recognised mental health condition.
The behavioural, emotional and cognitive features of depression cannot therefore be dismissed simply because depression is relatively common.
Example 5: unusual dress
A person wears clothes that are uncommon within their community.
Statistical infrequency could identify the clothing as unusual.
It cannot determine whether the person has a mental health difficulty.
The behaviour may reflect:
Personal taste.
Religious belief.
Cultural identity.
Artistic expression.
Membership of a social group.
This example may be understood more effectively using expectations within cultures and social situations.
Choosing an appropriate population
The reference group
A judgement of statistical infrequency depends on the population used for comparison.
This is called the reference group.
A behaviour could be rare in one group but common in another.
Relevant groups might be based on:
Age.
Culture.
Occupation.
Developmental stage.
Education.
Social circumstances.
Age differences
Some behaviours are common at one age but unusual at another.
For example, reliance on adults for everyday care is:
Expected in a young child.
Less common in an independent adult.
A statistical judgement must therefore compare the person with an appropriate age group.
Cultural differences
A behaviour that appears infrequent in one cultural group may be more common in another.
If statistics are collected from only one cultural group, they may not provide a fair standard for everyone.
This could lead psychologists to misclassify culturally typical behaviour as unusual.
Outdated statistics
Population patterns can change.
Statistics may become inaccurate because of changes in:
Awareness.
Diagnosis.
Reporting.
Social attitudes.
Access to healthcare.
Population characteristics.
Statistical infrequency therefore relies on accurate and up-to-date information.
Official mark-scheme guidance identifies the need for current statistics as part of this definition.
Prevalence
What is prevalence?
Prevalence refers to how common a behaviour, characteristic or condition is within a population.
A prevalence figure may state:
The number of people affected.
The proportion of a population affected.
The percentage affected during a particular period.
Statistical infrequency uses prevalence to decide whether something is common or rare.
Low prevalence does not always mean disorder
A characteristic may have low prevalence because it is:
An exceptional strength.
A harmless personal difference.
A rare preference.
A specialised skill.
Low prevalence only establishes rarity.
High prevalence does not mean healthy
A behaviour or condition may be common but still:
Cause distress.
Reduce quality of life.
Disrupt work or education.
Require professional support.
This means frequency and psychological wellbeing are different questions.
Strengths of statistical infrequency
Strength: it is based on numerical data
Statistical infrequency uses measurable information.
Psychologists can:
Count how many people display a characteristic.
Calculate averages.
compare scores.
identify extreme values.
examine population distributions.
This can make the definition appear more objective than one based only on personal opinion.
Why objectivity is useful
Numerical criteria can improve consistency.
Two professionals using the same:
Assessment.
Reference population.
Scoring system.
Cut-off point.
should be more likely to reach similar conclusions.
This can improve reliability.
Strength: it can be useful in assessment
Statistical information can help identify people whose scores are sufficiently unusual to require further assessment.
For example, an extremely low cognitive score may indicate that a person could benefit from:
Educational support.
Additional assessment.
Adaptations.
Practical assistance.
The definition can therefore have useful real-world applications.
Strength: it allows comparisons
Statistical data allow psychologists to compare:
One person with a population.
Different groups.
Different ages.
Changes over time.
Scores before and after support.
Without a statistical standard, it may be difficult to determine how unusual a score actually is.
Strength: it avoids some social judgements
A numerical definition does not initially ask whether behaviour is:
Proper.
Moral.
Fashionable.
Socially approved.
This may reduce some of the value judgements involved in deviation from social and cultural norms.
However, value judgements are not removed completely because someone must still choose:
What to measure.
Which population to use.
Where to place the cut-off.
What consequences should follow.
Strength: statistics are used in real identification
Many forms of psychological assessment include comparisons with population norms.
This suggests that statistical information has genuine practical value.
Official AQA mark-scheme guidance recognises that diagnoses may involve some reference to statistical information.
Statistical infrequency is therefore not useless.
Its weakness is using rarity as the only criterion.
Limitations of statistical infrequency
Limitation: some unusual characteristics are desirable
An infrequent characteristic is not necessarily harmful.
Examples could include:
Exceptional intelligence.
Exceptional memory.
Outstanding musical ability.
Unusually high resilience.
Exceptional athletic ability.
These characteristics are rare but may be valued.
This creates a problem for the claim:
Rare equals psychologically abnormal.
A more accurate conclusion is:
Rare means statistically unusual, but further information is needed to decide whether the characteristic represents a mental health difficulty.
Limitation: some mental health conditions are common
Some recognised mental health conditions affect a substantial number of people.
If a condition becomes common, statistical infrequency might fail to identify it as unusual.
This would create the strange conclusion that:
A condition stops being a mental health problem once enough people experience it.
Frequency therefore cannot be the sole basis for defining mental health.
The AQA examiner report identifies depression as an effective example of a condition that may be relatively frequent but should not therefore be considered psychologically healthy.
Limitation: the cut-off point may be arbitrary
Psychologists must decide how unusual a score must be before it is classified as abnormal.
A cut-off may be useful administratively, but two people on either side of the boundary could be almost identical.
For example:
Person A scores just inside the chosen range.
Person B scores one point beyond it.
It may be difficult to justify treating the two people as fundamentally different.
The definition can therefore create artificial categories from continuous differences.
Limitation: it does not consider distress
A rare behaviour may not trouble the person at all.
Statistical infrequency does not ask whether the person:
Feels anxious.
Experiences low mood.
Wants support.
Is frightened by the behaviour.
Feels unable to cope.
A person could be statistically unusual but perfectly content.
Limitation: it does not consider everyday functioning
The definition does not tell us whether the characteristic interferes with:
Work.
Education.
Relationships.
Self-care.
Safety.
Everyday responsibilities.
A rare behaviour that has no effect on daily life may not require intervention.
A common behaviour that severely disrupts daily functioning may be much more important.
This is why psychologists may also consider failure to function adequately.
Limitation: it may label harmless differences
Describing statistically unusual people as abnormal can create:
Stigma.
Unnecessary concern.
Pressure to become more typical.
Unhelpful labels.
Discrimination.
Human diversity naturally includes uncommon characteristics.
Rarity should not automatically be treated as a defect.
Limitation: statistics depend on the sample
Population statistics are usually based on a sample rather than every individual.
If the sample is unrepresentative, the estimated frequency may be inaccurate.
A sample might underrepresent people from:
Particular cultural groups.
Particular age groups.
Rural communities.
People without access to healthcare.
People unwilling to report symptoms.
The definition can be only as accurate as the data used.
Limitation: recorded frequency may differ from actual frequency
A behaviour may appear rare because people:
Hide it.
Do not recognise it.
Do not seek professional help.
Fear stigma.
Lack access to assessment.
Are diagnosed incorrectly.
Recorded prevalence may therefore underestimate how common the behaviour really is.
Limitation: statistics can change over time
A characteristic may appear more common because:
Awareness improves.
Diagnostic systems change.
More people seek help.
Reporting becomes less stigmatised.
Assessment becomes more accessible.
If the statistical definition relies on outdated data, people may be judged against an inaccurate standard.
Limitation: it gives little explanation
Statistical infrequency describes how rare a characteristic is.
It does not explain:
Why it developed.
What maintains it.
Whether it will continue.
How it should be treated.
Whether the person needs support.
It is a definition, not a psychological explanation.
Objective does not mean value-free
Numerical measurement
The person’s score may be measured objectively.
For example:
A score is calculated.
A frequency is counted.
A position in a distribution is identified.
Subjective decisions
Human judgement is still involved in deciding:
Which characteristic matters.
Which assessment should be used.
Which population is appropriate.
How rare is rare enough.
Whether being unusual should be treated as a problem.
Statistical infrequency is therefore relatively objective, but not completely free from values.
Comparing statistical infrequency with other definitions
The AQA specification requires four definitions in the field of mental health:
Statistical infrequency.
Deviation from social and cultural norms.
Failure to function adequately.
Deviation from ideal mental health.
Comparison table
Definition | Main question asked | Key strength | Key limitation |
Statistical infrequency | Is the behaviour rare? | Numerical and measurable | Rare does not always mean harmful |
Deviation from social and cultural norms | Does the behaviour break social expectations? | Considers behaviour in context | Norms vary across cultures and time |
Failure to function adequately | Can the person manage ordinary life? | Considers distress and practical effects | Judgements about adequate functioning may be subjective |
Deviation from ideal mental health | Does the person meet positive standards of wellbeing? | Focuses on psychological health, not just illness | The ideal may be unrealistically demanding |
Why several definitions are useful
No single definition is sufficient in every situation.
A more complete judgement may consider:
How rare the behaviour is.
Whether it causes distress.
Whether it prevents everyday functioning.
Whether it creates danger.
Whether it breaks important norms.
Whether it reflects poor psychological health.
For example, a rare characteristic might attract attention through statistical infrequency.
A psychologist could then consider whether it also involves:
Failure to function.
Distress.
Departure from ideal mental health.
Applying more than one definition
Example: exceptional memory
An individual has an exceptionally rare memory ability.
Statistical infrequency: The ability is unusual.
Failure to function adequately: The person manages everyday life successfully.
Deviation from ideal mental health: The characteristic does not necessarily indicate poor wellbeing.
Conclusion: the person is statistically unusual, but there is little reason to identify a mental health difficulty.
Example: common but disabling anxiety
Many people experience anxiety, so the experience may not be extremely rare.
However, one person’s anxiety prevents them from:
Leaving home.
Attending college.
Maintaining friendships.
Completing ordinary tasks.
Statistical infrequency may be less helpful here.
Failure to function adequately provides more relevant information.
Example: unusual belief
A belief is held by very few people within one population.
Statistical infrequency identifies it as rare.
However, before judging it, psychologists should consider:
The person’s culture.
Religious context.
Whether the belief causes distress.
Whether it affects functioning.
Whether it is shared by an appropriate cultural group.
Frequency alone may produce a culturally unfair conclusion.
How to answer application questions
Application structure
Use the following structure:
Identify the behaviour or score.
Compare it with the population.
State whether it is common or rare.
Explain why it is statistically infrequent.
Consider whether rarity is sufficient to indicate a mental health difficulty.
Weak application
The behaviour is abnormal because it is weird.
This response:
Does not use statistical terminology.
Makes a value judgement.
Does not refer to frequency.
Does not compare the individual with a population.
Stronger application
The behaviour would be statistically infrequent because it occurs in only a very small proportion of the relevant population. It lies at an extreme rather than close to the typical pattern. However, rarity alone does not show that it causes distress or difficulty.
Applying numerical information
Suppose a study finds:
Behaviour | Percentage of population showing it |
Behaviour A | 68% |
Behaviour B | 19% |
Behaviour C | 2% |
Behaviour C is the most statistically infrequent because it occurs in the smallest proportion of the population.
However, the table does not show whether Behaviour C is:
Helpful.
Harmful.
Distressing.
Associated with mental health.
The conclusion must remain limited to frequency.
How to evaluate the definition effectively
Point, evidence and explanation
A developed evaluation paragraph should include:
A clear strength or limitation.
A relevant example.
An explanation of why the point affects the usefulness of the definition.
A reasoned conclusion.
Weak evaluation
Statistical infrequency is bad because rare things can be good.
Stronger evaluation
Statistical infrequency may incorrectly classify desirable characteristics as abnormal. Exceptionally high intelligence is rare and lies at an extreme of the distribution, yet it is generally valued rather than regarded as a mental health difficulty. This shows that rarity alone does not distinguish beneficial differences from psychological problems.
Another developed limitation
The definition may fail to recognise common mental health conditions. Depression affects many people, so it is not necessarily statistically rare, yet it can cause severe distress and disruption. Statistical infrequency therefore lacks sensitivity when the condition is widespread and should be combined with another definition.
Developed strength
Statistical infrequency provides measurable criteria because a person’s score can be compared with population data. This may improve consistency between professionals and is useful when identifying extreme cognitive scores. However, numerical measurement does not remove the need to choose a cut-off point.
Reaching a balanced judgement
Statistical infrequency is most useful when:
The characteristic can be measured accurately.
Reliable population statistics are available.
An extreme score is relevant to support or assessment.
The reference population is appropriate.
Other information is also considered.
It is least useful when:
The rare characteristic is desirable.
A genuine disorder is common.
The person is not distressed or impaired.
The population data are outdated.
Cultural differences are ignored.
An arbitrary cut-off creates an artificial label.
The most justified conclusion is:
Statistical infrequency is a useful way to identify unusual scores and behaviours, but it cannot define mental health successfully when used alone.
Hints from the Examiner Reports 💡
Examiner hint: Define the concept precisely. State that statistical infrequency identifies behaviour or characteristics that are rare, uncommon or located at the extremes of a distribution.
Examiner hint: Use a genuinely psychological example. Examiner commentary noted that weak answers sometimes used physical characteristics such as body weight without clearly linking them to behaviour or mental health.
Examiner hint: Exceptionally high intelligence is an effective limitation because it is statistically rare but usually desirable.
Examiner hint: Depression is a useful contrasting example because a condition can be relatively common while still involving serious psychological difficulty.
Examiner hint: Do not confuse the four definitions. Statistical infrequency concerns rarity, whereas deviation from social norms concerns breaking expectations.
Examiner hint: Develop evaluation points. Do not stop after writing “some rare behaviours are good”. Explain why this means rarity cannot distinguish unusual strengths from mental health difficulties.
Examiner hint: Alternative definitions can be used to evaluate statistical infrequency. For example, failure to function adequately considers whether the behaviour disrupts everyday life.
Examiner hint: When applying data, describe only what the figures show. A low percentage demonstrates rarity but does not by itself prove distress, danger or a disorder.
The Autumn 2021 examiner report found that stronger answers used relevant psychological examples and alternative definitions, while weaker responses confused statistical infrequency with other definitions or used examples without explaining their relevance.
Common Mistakes ⚠️
Mistake: Saying that all rare behaviour is a mental disorder
Why this is incorrect:
Rare characteristics may be desirable, harmless or valuable.
How to improve:
State that statistical rarity identifies unusualness but not necessarily psychological difficulty.
Mistake: Saying that all mental health conditions are rare
Why this is incorrect:
Some recognised conditions are relatively common.
How to improve:
Use depression as an example of why frequency alone is insufficient.
Mistake: Defining statistical infrequency as breaking social rules
Why this is incorrect:
Breaking expectations relates to deviation from social and cultural norms.
How to improve:
Focus on how frequently the behaviour occurs in a population.
Mistake: Saying that a behaviour is abnormal because it is strange
Why this is not a statistical explanation:
“Strange” is a subjective judgement.
How to improve:
Refer to prevalence, population data or position within a distribution.
Mistake: Ignoring the reference population
Why this is a problem:
A behaviour may be common in one age or cultural group but rare in another.
How to improve:
Identify the appropriate population used for comparison.
Mistake: Assuming a cut-off is completely objective
Why this is inaccurate:
The score may be numerical, but someone must decide where the boundary should be placed.
How to improve:
Distinguish objective measurement from subjective classification decisions.
Mistake: Saying high IQ proves statistical infrequency is useless
Why this is too extreme:
The definition remains useful for identifying unusual scores.
How to improve:
Conclude that it is useful but incomplete when used alone.
Mistake: Using a physical example without linking it to mental health
Why this may not gain credit:
The question concerns a definition in the field of mental health.
How to improve:
Choose an example such as an extreme cognitive score or explain clearly why the characteristic is psychologically relevant.
Mistake: Assuming a low percentage proves a disorder
Why this is incorrect:
A percentage shows frequency, not distress or impairment.
How to improve:
Limit the conclusion to statistical rarity and consider another definition.
Mistake: Ignoring desirable rarity
Why this weakens evaluation:
The definition treats both extremes as unusual.
How to improve:
Compare exceptionally low and exceptionally high scores.
Mistake: Ignoring common disorders
Why this weakens evaluation:
A common condition could be missed by a rarity-based definition.
How to improve:
Explain why prevalence and psychological harm are not the same.
Mistake: Describing standard deviation without linking it to the definition
Why this is incomplete:
Research-method knowledge earns value only when it explains statistical rarity.
How to improve:
Explain that scores far from the mean occur less frequently.
Mistake: Listing other definitions without comparison
Why this is ineffective evaluation:
Simply naming them does not explain why they improve on statistical infrequency.
How to improve:
State what additional information each definition considers, such as distress or everyday functioning.
Exam-Style Questions ✍️
Question 1
Which one of the following best describes statistical infrequency?
A. Behaviour that causes distress to the individual
B. Behaviour that breaks the rules of a society
C. Behaviour or characteristics that occur rarely within a population
D. Behaviour that prevents a person from reaching ideal mental health
[1 mark]
reveal mark scheme and indicative content
Answer: C. Behaviour or characteristics that occur rarely within a population
Question 2
Define statistical infrequency as a definition in the field of mental health.
[2 marks]
reveal mark scheme and indicative content
Mark scheme
AO1 = 2
2 marks: Clear definition referring to behaviour or characteristics being considered unusual because they are statistically rare within a population.
1 mark: Limited or partial definition.
Indicative content
Focuses on how frequently a behaviour or characteristic occurs.
Rare or uncommon characteristics are considered statistically unusual.
May involve comparison with population norms.
Example answer
Statistical infrequency defines behaviour or characteristics as unusual when they occur rarely within a population compared with what is statistically typical.
AQA defines statistical infrequency in terms of behaviour or characteristics that are rare, uncommon or anomalous.
Question 3
Explain why the normal distribution is relevant to statistical infrequency.
[3 marks]
reveal mark scheme and indicative content
Mark scheme
AO1 = 3
Award 1 mark each for:
Many measurable characteristics can be represented using a normal distribution.
Most people's scores occur around the mean or centre of the distribution.
Scores towards the extreme ends are much less frequent and can therefore be identified as statistically unusual.
Example answer
In a normal distribution, most people's scores cluster around the mean, while progressively fewer scores occur towards the extremes. Statistical infrequency therefore identifies scores at the extreme ends of the distribution as unusual because very few people obtain them.
AQA specifically credits the idea that statistically infrequent characteristics occupy the extreme ends of a normal distribution curve.
Question 4
An individual obtains a score at the extreme lower end of a standardised cognitive assessment.
Use statistical infrequency to explain why the score might lead to further assessment.
[4 marks]
reveal mark scheme and indicative content
Mark scheme
AO2 = 4
Award 1 mark each for:
The person's score is at the extreme lower end of the distribution.
Very few members of the population would obtain a similar score.
The score is therefore statistically infrequent.
Its rarity could justify further assessment, although the score alone would not necessarily demonstrate a mental health or developmental difficulty.
Example answer
The score is at the extreme lower end of the distribution, so very few people in the population are likely to obtain it. Statistical infrequency would therefore identify the score as unusual. This could indicate that further assessment is appropriate, although statistical rarity by itself would not be enough to establish that the person has a difficulty.
Question 5
An individual has an exceptionally high IQ score that is achieved by very few people.
Explain why this example creates a problem for statistical infrequency as a definition in the field of mental health.
[4 marks]
reveal mark scheme and indicative content
Mark scheme
AO3 = 4
Award 1 mark each for:
A very high IQ is statistically infrequent.
Statistical infrequency alone could therefore classify it as unusual.
However, high IQ is generally considered desirable rather than evidence of a mental health difficulty.
Therefore, rarity alone cannot distinguish between desirable and undesirable characteristics.
Example answer
An exceptionally high IQ is statistically infrequent because very few people achieve it. However, a high IQ is generally regarded as desirable rather than evidence of a mental health difficulty. This shows that simply being statistically rare is not sufficient for identifying psychological problems.
AQA explicitly identifies very high IQ as an example of statistically rare but desirable behaviour or characteristics.
Question 6
A researcher records the following results:
Behaviour | Percentage of the population displaying it |
Behaviour A | 57% |
Behaviour B | 14% |
Behaviour C | 3% |
Identify which behaviour is the most statistically infrequent. Explain why the table alone cannot show whether the behaviour represents a mental health difficulty.
[4 marks]
reveal mark scheme and indicative content
Mark scheme
AO2/AO3 = 4
Award 1 mark each for:
Behaviour C is the most statistically infrequent.
It occurs in only 3% of the population, compared with 14% and 57%.
Frequency alone does not indicate whether a behaviour is harmful, undesirable or associated with mental health difficulties.
Additional information about factors such as distress, functioning or the nature of the behaviour would be needed.
Example answer
Behaviour C is the most statistically infrequent because it occurs in only 3% of the population. However, the table only shows how common each behaviour is. A rare behaviour could be positive or harmless, so information about its effects on the person and their functioning would also be needed before deciding whether it represents a mental health difficulty.
Question 7
A student says:
“Depression cannot be a mental health condition because many people experience it.”
Use your knowledge of statistical infrequency to explain why the student’s conclusion is incorrect.
[4 marks]
reveal mark scheme and indicative content
Mark scheme
AO3 = 4
Award 1 mark each for:
Statistical infrequency considers rarity, but this definition has limitations.
Some recognised mental health conditions are relatively common.
A behaviour or set of symptoms does not stop being clinically significant simply because many people experience it.
Other definitions or criteria, such as distress and ability to function, may therefore also need to be considered.
Example answer
The student's conclusion is incorrect because statistical infrequency is only one way of defining difficulties in mental health. Some recognised conditions, such as depression, can affect many people and therefore may not be statistically rare. Their frequency does not mean that they cannot cause significant distress or difficulty functioning.
AQA examiner feedback specifically highlights depression being relatively frequent
rather than infrequent as an effective criticism of statistical infrequency.
Question 8
Explain one strength and one limitation of statistical infrequency as a definition in the field of mental health.
[6 marks]
reveal mark scheme and indicative content
Mark scheme
AO3 = 6
Award up to 3 marks for the strength and 3 marks for the limitation.
Indicative content
Strength
Statistical infrequency can provide an objective, numerical basis for identifying unusual characteristics.
Standardised scores can be compared with population norms.
This may be useful in clinical or educational assessment when identifying people who may require further investigation or support.
Limitation
Statistical rarity does not necessarily mean that a characteristic is undesirable.
Very high IQ is statistically rare but usually valued.
Conversely, some genuine mental health difficulties may be relatively common.
Therefore, frequency alone is insufficient.
Example answer
One strength is that statistical infrequency can provide an objective way of identifying unusual characteristics. A person's score can be compared with population data, making the judgement less dependent on individual opinion and potentially helping identify people who need further assessment.
One limitation is that statistically rare characteristics are not always undesirable. For example, an exceptionally high IQ is rare but generally considered positive. Therefore, statistical infrequency alone cannot reliably distinguish mental health difficulties from desirable differences.
AQA explicitly credits both the usefulness of statistics in identifying some difficulties and the problem of statistically rare but desirable characteristics
Question 9
A psychologist classifies everyone beyond a particular score as psychologically abnormal.
Explain one problem with using a fixed statistical cut-off point.
[4 marks]
reveal mark scheme and indicative content
Mark scheme
AO3 = 4
Award credit for one clearly developed problem.
Indicative content
The point at which a score changes from statistically typical to statistically unusual can be arbitrary.
People immediately either side of the cut-off may have almost identical scores.
Yet one person may be classified as unusual while the other is not.
This can create an artificial distinction in a characteristic that actually varies continuously.
AQA explicitly identifies the difficulty of deciding where the line should be drawn between statistically normal and unusual.
Example answer
One problem is that the cut-off may be arbitrary. Two people could obtain almost identical scores but fall just either side of the boundary, meaning one is classified as statistically unusual while the other is not. This creates an artificial distinction when the characteristic actually varies along a continuum.
Question 10
Discuss statistical infrequency as a definition in the field of mental health.
[8 marks]
reveal mark scheme and indicative content
Mark scheme
Suggested allocation: AO1 = 3, AO3 = 5
7 to 8 marks: Knowledge of statistical infrequency is accurate and detailed. Discussion is thorough, relevant and well developed. Specialist terminology is used effectively.
5 to 6 marks: Knowledge is generally accurate and discussion is mostly effective, although some points lack development.
3 to 4 marks: Some relevant knowledge is present but the response is mainly descriptive or evaluation is limited.
1 to 2 marks: Very limited knowledge or discussion.
0 marks: No relevant content.
Indicative content
AO1
Statistical infrequency focuses on behaviours or characteristics that are rare or uncommon within a population.
Population statistics can be used to establish what is typical.
Statistically unusual scores may occur at the extremes of a normal distribution.
An example is an extremely low score on a standardised cognitive assessment.
Statistics need to be current and appropriate to the population being assessed.
AO3
Objectivity: numerical population data provide a relatively objective basis for identifying unusual characteristics.
Practical usefulness: statistical criteria can help identify individuals who may benefit from further assessment or support.
Desirable rarity: some statistically infrequent characteristics, such as very high IQ, are positive rather than evidence of difficulty.
Common conditions: some recognised mental health conditions, such as depression, may not be particularly rare.
Arbitrary boundaries: deciding where to place the cut-off between typical and statistically unusual can be subjective.
Statistics change: prevalence and population norms may change over time, so outdated statistics can lead to inaccurate judgements.
Statistical infrequency may therefore be most useful when considered alongside other definitions, such as failure to function adequately.
These evaluation points closely reflect AQA's published guidance, including desirable rare characteristics, common disorders, difficulty setting cut-offs and the need for up-to-date statistics.
Example answer
Statistical infrequency defines behaviour or characteristics as unusual when they occur rarely within a population. Many measurable characteristics can be represented using a normal distribution, with most scores around the mean and relatively few at the extremes. An extremely low score on a standardised cognitive assessment could therefore be identified as statistically unusual.
One strength is that the definition uses numerical population data, providing a relatively objective way of identifying unusual characteristics. It can therefore be useful for deciding when further assessment may be needed. However, statistical rarity does not necessarily indicate a mental health difficulty. An exceptionally high IQ is rare but generally desirable. The reverse problem also occurs because some genuine mental health conditions, such as depression, are relatively common. There is also difficulty deciding exactly where a statistical cut-off should be placed, as people just either side of it may be very similar. Statistical infrequency is therefore useful for identifying unusual characteristics, but it should not usually be relied upon alone when judging mental health.
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