Normal iq range
Pro Research Analysisby 
Searched over 200M research papers
Understanding the Normal IQ Range
Definition and Measurement of IQ
Intelligence Quotient (IQ) is a standardized measure used to assess human intelligence. The average IQ score is set at 100, with the majority of the population scoring within a range that is considered "normal." This range typically spans from 85 to 115, encompassing about 68% of the population2 4 6.
Variations in Normal IQ
Gender Differences in IQ
Research indicates that there are slight variations in IQ scores between genders. For instance, a study examining the relationship between IQ and common childhood psychopathology found that the mean IQ was 6.0 points lower for females than males in cases of conduct and emotional disorders2. However, these differences are generally small and do not significantly impact the overall distribution of IQ scores within the normal range.
Birth Weight and IQ
Another factor influencing IQ within the normal range is birth weight. A cohort study found that IQ at age 7 years is linearly related to birth weight among children of normal birth weight. This relationship was particularly evident in boys, where differences in birth weight were directly associated with differences in IQ4. This suggests that even within the normal birth weight range, higher birth weights can be associated with slightly higher IQ scores.
IQ and Learning Disabilities
Learning Disabilities and IQ Scores
Children with learning disabilities often have IQ scores that fall within the low-average to high-average range. Studies have shown that the average IQ score of many learning disability samples is significantly below 100, although still above the threshold for mental retardation3 6. This indicates that while these children may struggle with specific academic skills, their overall cognitive abilities can still fall within the normal range.
Cognitive and Language Skills in Autism
For individuals with autism spectrum disorders (ASD) who have an IQ in the normal range, cognitive and language skills can vary widely. Longitudinal studies have shown that while many individuals with ASD maintain stable IQ scores into adulthood, a significant minority experience severe behavioral disturbances and language impairments that affect their functional abilities5 8. This highlights the variability in outcomes for individuals with normal-range IQs who have developmental disorders.
High IQ and Its Implications
Extremely High IQ
Extremely high IQ, defined as scores significantly above the average, is also a subject of interest. A genome-wide association study found that individuals with extremely high IQs (around 170) share genetic correlations with educational attainment and population IQ, suggesting that high intelligence is genetically continuous with normal-range intelligence9. This implies that the factors contributing to high IQ are extensions of those influencing normal IQ.
Norms for Highly Intelligent Adults
For highly intelligent adults (IQ ≥ 120), normative data from neuropsychological tests can help identify typical cognitive performance and detect abnormal cognitive decline. This is particularly useful for clinicians working with individuals at risk for progressive dementia7.
Conclusion
The normal IQ range, typically between 85 and 115, encompasses a wide variety of cognitive abilities and is influenced by factors such as gender, birth weight, and the presence of learning disabilities or developmental disorders. While most individuals with normal-range IQs function well, there are significant variations that can impact educational and life outcomes. Understanding these variations helps in providing better support and interventions for those at the lower or higher ends of the normal IQ spectrum.
Sources and full results
Most relevant research papers on this topic
A systematic literature review of the average IQ of sub-Saharan Africans
The average IQ of sub-Saharan Africans is around 82, compared to UK norms, but more psychometric studies are needed to address measurement bias in western IQ tests.
Systematic Review
Highly CitedThe relationship between normal variation in IQ and common childhood psychopathology: A clinical study
The mean IQ is 9.6 points lower for conduct disorders than emotional disorders, with mixed disorders in between, and 6.0 points lower for girls than boys.
Numerical and arithmetical cognition: a longitudinal study of process and concept deficits in children with learning disability.
Children with learning disabilities show specific cognitive deficits in mathematics and reading, beyond the influence of IQ.
Non-RCTHighly CitedInfluence of variation in birth weight within normal range and within sibships on IQ at age 7 years: cohort study
IQ at age 7 years is linearly related to birth weight in children of normal birth weight, with a stronger association for boys within same sex sibships.
Observational StudyHighly CitedCognitive and language skills in adults with autism: a 40-year follow-up.
Childhood IQ is a reliable predictor of cognitive functioning in adults with autism, but a significant minority remains untestable due to severe behavioral disturbances and language impairments.
Observational StudyHighly CitedThe Bivariate Normal Distribution and the IQ of Learning Disability Samples
The average IQ score of learning disability samples is significantly below 100 due to the relationship between achievement and IQ, with correlations between achievement and IQ increasing as the average IQ score decreases.
IQ-Based Norms for Highly Intelligent Adults
Highly intelligent adults (IQ 120) exhibit typical cognitive performance, which can help clinicians identify abnormal cognitive decline in individuals at risk for progressive dementia.
Observational StudyAdult outcome for children with autism.
Adults with autism have improved outcomes, but many remain highly dependent on others for support, with childhood performance IQ being a variable prognostic indicator.
Observational StudyHighly CitedA genome-wide association study for extremely high intelligence
Extremely high intelligence is genetically continuous with normal-range intelligence in the population, with three variants in locus ADAM12 showing genome-wide significance.
Observational Study
Rigorous JournalIntelligence: new findings and theoretical developments.
Intelligence is influenced by both biological and social factors, with the IQ gap between Blacks and Whites narrowing by 0.33 SD in recent years.
Literature ReviewHighly CitedTry another search
What are the ethical considerations in anthropological research and practice?
What are the causes and consequences of globalization on cultures and societies?
What are the applications of nanotechnology in sensing and diagnostics?
operant conditioning
What are the challenges faced when developing a project business case for projects like the UN slum
What are the different types of energy conversion technologies?