Seven million people with borderline intellectual functioning: is that a count of diagnoses?

The figure of approximately 7 million people with borderline intellectual functioning is not a count of people who have actually been diagnosed or registered. It is an arithmetic estimate obtained by applying the 13.6% proportion from a normal IQ distribution to South Korea's resident-registration population in July 2026.[1][2][5]

At first, I also thought this was a count of actual individuals. But tracing the sources and calculations showed that it meant something different from the approximately 2.13 million and 1.58 million estimates based on a Korean screening survey.[3][5]

A nationwide Korean screening survey has also recently become available, providing data that should be distinguished from this theoretical figure. The two sources are not measuring the same population.[3]

First, here are the three figures side by side.

“Exploratory group” and “at-risk group” below are the classification labels used in the screening-survey report.[3]

- Approximately 6.95 million: the theoretical population range implied by a normal IQ distribution[1][2][5]

- Approximately 2.13 million: an expanded screening-based estimate combining the exploratory and at-risk groups among people aged 7-59[3][5]

- Approximately 1.58 million: an estimated at-risk group within the same age range for whom further comprehensive assessment could be considered a priority[3][5]

None of these three figures is a count of confirmed diagnoses.[1][2][3]

1. Where did the figure of approximately 7 million come from?

Traditionally, borderline intellectual functioning has been described in relation to an IQ range of approximately 71-84. Assuming IQ follows a normal distribution with a mean of 100 and a standard deviation of 15, the interval 1-2 standard deviations below the mean accounts for approximately 13.59%. This is commonly rounded to 13.6%.[1][2]

On July 31, 2026, South Korea's resident-registration population was 51,088,284. Applying 13.6% gives the following.[5]

51,088,284 people × 13.6% = 6,948,007 people

This calculation produces the expression “approximately 6.95 million,” or, more simply, “approximately 7 million.”[1][2][5]

No individual test results are included in this calculation. Nor does it account for differences in region, age, educational experience, language and culture, or adaptive functioning. It is simply a theoretical scenario that multiplies the entire population by the same proportion.

Current clinical judgment is not based on an IQ score alone either. Adaptive functioning, developmental context, and measurement error also need consideration.[1][2]

It is therefore inappropriate to write, “There are exactly 6.95 million people with borderline intellectual functioning in South Korea.”

2. Are there data collected directly in Korea?

I also looked for Korean data separately. I have not yet identified national statistics showing the entire population with confirmed or registered borderline intellectual functioning. However, it would now also be wrong to say that “there are no nationwide data at all.”[3][4]

In 2025, the Ministry of Health and Welfare and the Korea Institute for Health and Social Affairs published a survey of the circumstances of people with borderline intellectual functioning. It was conducted with a nationwide online panel between January and March 2025, and the final sample in the age table comprised 9,019 people.[3]

The survey covered people from the first year of elementary school through age 59. It used screening checklists based on parents' observations for children and adolescents, and self-reports for adults.[3]

This part requires particular care when reading the findings.

Even those classified as at risk in the survey had not received a formal diagnosis through the survey.[3]

They were a screening-identified group for whom further standardized intelligence testing and assessment of adaptive functioning might need to be considered.[3]

Applying the report's age-specific rates to the 2026 resident-registration population produces the following arithmetic estimates within the population of 34,014,465 people aged 7-59, aligned with the survey's scope.[3][5]

- Expanded at-risk population combining the exploratory and at-risk groups: approximately 2,125,163 people[3][5]

- At-risk group: approximately 1,577,723 people[3][5]

The expanded at-risk population represents approximately 6.25% of the population in that age range.[3][5]

These rates were not applied to ages 0-6 or to people aged 60 and above, who were outside the survey's scope. The approximately 2.13 million figure should therefore not be used as an established total for all ages in South Korea.[3]

3. How do 6.95 million, 2.13 million, and 1.58 million differ?

Putting the figures side by side made the differences clearer.

The approximately 6.95 million figure is a separate theoretical estimate.[1][2]

By contrast, the approximately 1.58 million figure is included within the approximately 2.13 million figure from the same screening survey.[3][5] The three figures are not successive stages of narrowing down a single population from the largest number.

Approximately 6.95 million describes a theoretical population range derived by applying a normal IQ distribution to the total population. It can be useful for comparing broad population scales across countries using the same formula, but it is neither a diagnosed population nor the number of people who would immediately use a service.[1][2][5]

Approximately 2.13 million is an expanded estimate obtained by applying the Korean screening survey's exploratory-group and at-risk-group rates to the population in the surveyed age range.[3][5] This is based on Korean screening data, distinct from the theoretical 13.6%, but it is not the same as actual service demand or a count of diagnoses.

Approximately 1.58 million estimates the at-risk group within that figure, excluding the exploratory group.[3][5] It can serve as a reference when exploring the possible scale of the need for further comprehensive assessment.

None of these figures answers the question, “How many people have actually been diagnosed?”[1][2][3]

4. Why the labels attached to numbers matter

Mislabeling a number can change decisions about policy and business.

Treating all approximately 7 million people as immediately needing the same service could exaggerate demand. Conversely, downplaying support needs because there are no confirmed diagnosis statistics could overlook people who repeatedly struggle in education and working life while remaining outside existing systems.

Particularly when discussing work and independent living for people with borderline intellectual functioning, we need to consider difficulties in actual performance, adaptive functioning, and the types and intensity of support needed, rather than defining the population solely by an IQ range.

I think it is more honest and practical to explain which figure is being used for which purpose than to repeat one large number.

5. A more careful way to present the figures

When including these figures in a report, article, or business plan, I would write them as follows.

“Applying the 13.6% proportion from a normal IQ distribution to the resident-registration population in July 2026 yields an arithmetic estimate of approximately 6.95 million people in the borderline intellectual functioning range. This is not a diagnosed population. Applying the age-specific rates from the 2025 national screening survey gives an estimated at-risk group of approximately 1.58 million among the surveyed ages of 7-59, and an expanded at-risk population of approximately 2.13 million when the exploratory group is included.”

By contrast, it is better to avoid the following wording.

“There are exactly 6.95 million people with borderline intellectual functioning in South Korea.”

Sources and calculation basis

- Resident-registration population reference date: July 31, 2026

- Theoretical scenario: total resident-registration population × 13.6%

- Korean screening data: Ministry of Health and Welfare and Korea Institute for Health and Social Affairs, Survey of the Circumstances of People with Borderline Intellectual Functioning

- Ages included in the screening-based estimates: 7-59

- Calculation of person counts: apply the rates to the underlying population, then round

The figures in this article are not counts of directly diagnosed individuals, registered individuals, or service users.

When using them to design policies or services, the definition of the population and the scope of the survey should be stated together.

Slowcoach organizes data and questions from practice about work and independent living for people with borderline intellectual functioning. If you have a question about interpreting these figures or applying them in practice that you would like to explore together, please leave a comment.