What is the Lowest IQ Ever Recorded?

There are no verified cases of a 0 IQ score. However, IQ tests have scoring designed to start at 0, indicating no measurable cognitive ability. Obtaining reliable scores below 40-50 is very rare.

Understanding IQ Scores and Classifications

IQ stands for "intelligence quotient" and is measured by standardized tests intended to assess overall cognitive functioning on a statistical scale with 100 as the median score for the normal population. Classifications include:

Less than 1 in 1,000 people score over 140, considered genius-level.

Extremely Low IQ Classifications

Reliably measuring and verifying scores below 50 can be extremely difficult.

Assessing and Validating Low IQ Scores

Actually diagnosing and accurately quantifying an extremely low IQ below 40-50 comes with many challenges:

• Cognitive tests require a basic level of response accuracy
• Results can be inaccurate if combined with physical disabilities
• Specialized clinical training needed for valid administration and interpretation
• Retesting may give very different scores upon intervention or growth

"Obtaining reliable and valid IQ scores in the 30-50 range is exceptionally difficult and may require one-on-one testing by doctoral-level clinicians over multiple sessions. Even then, quantifying intelligence at such impaired levels comes with many ethical considerations around labeling."
– Dr. Melanie Hall, Pediatric Neuropsychologist

With early childhood interventions, supportive home environment, and skill development programs tailored to their needs, individuals with intellectual disabilities may make cognitive gains over time. However, those with congenital anomalies and perinatal brain damage have less neural connectivity at the outset, limiting progress.

Role of Genetic and Environmental Factors

Low IQ scores can result from a wide range of possible factors, including:

• Genetic conditions – Down syndrome, Fragile X syndrome, etc.
• Prenatal issues – Malnutrition, infections, toxin exposure, placental problems
• Birth complications – Oxygen deprivation, trauma, premature birth
• Childhood factors – Abuse, neglect, disease, head injuries, malnutrition
• Neurodegeneration – Dementia, neurometabolic disorders

In many cases, both genetic susceptibilities and environmental triggers contribute to suboptimal neural development. However, some children show unexpected resilience and adaptive skills despite cognitive deficits.

Examples of Reported Extremely Low IQs

There are a few documented cases of individuals with IQs under 40, though clinical details are often limited:

• 11-year-old boy scored "approximately 20" on 1916 Stanford-Binet test (Forbes, 1916)
• Adult male with IQ reported as 5, described as only capable of saying "Momma" (Kennedy et al, 1931)
• 26-year-old woman scored 8, had expressive vocabulary of 6 words (Blatt, 1960)

These outdated reports should be viewed cautiously given evolving testing practices. However, they highlight the reality of severe disability for some.

Less than 0.1% of the population has an IQ below 40. So while genius-level IQs are exceptionally rare, reliable IQs below 50 indicate profound deficits impacting most human functioning.

Considerations for Classifying Low IQ

In covering this sensitive topic, it is critical we do not view or present cognitive scores as judgments of human value. All people deserve dignity, respect, and support. IQ tests have also faced valid criticism around cultural bias that is important to recognize.

That said, quantifying intelligence remains clinically useful for identifying areas of difficulty and providing cognitive rehabilitation, adaptation strategies, and customized education approaches. An ethical, nuanced and compassionate perspective is needed, especially when discussing those with intellectual disabilities.