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July 24, 2020

Some of this post has been redacted.

Context: I have worked with mentally retarded patients in a social care context and physics PhDs in a laboratory context.

██████ ███████████ ██ ███████ ██ ██ ██ ███ ████████ ██████████ █████ █ ██████████'█ ████ ($-2\sigma$). ██████ ████ ████ ███ ████████ █████████ █████ █ ██████████'█ ███████ ($-1\sigma$) ███ ██ ██████████ ███████████ ██████████. ██ █████ █████, 2.3% ██ █ ██████████ ██ ████████ ████████ ███ 84.1% ██ ███████████ ██████████.

███ ███ ██ █████ ███████ ██ ██ █████ ██ ████████ ██ ██████ ███ ████████ ████ ██ █████. ██ ███ ████ ██ ██ $+2\sigma$ ($\sigma\equiv\text{“standard deviation”}$) █████ ███ ████ ████ ██████ ████ ██ ██ ██ ███ ██ ████ (50.0% ██ ███ ██████████) ██ ████████ ████████ ████████ ██ ███. ██ ███ ███ $+3\sigma$ █████ ███ ████ ████ ██████ ████ ████ $+1\sigma$ █████ ███ ████ (84.1% of the population) ██ ████████ ████████ ████████ ██ ███ [1]. ██ ███ █████████, 13.6% ███ ████ ███ █████████ ██████████ "██████████ ██████ ███████████". ████ ████ ███████████, ███ ███ 2.3% ██ ███ ██████████ ██ ███████████ ████████.

Standard Deviation to Percent Diagram

At the time of writing, Wikipedia lists [2] the following signs of mental retardation. I have applied a strikethrough like this to arbitrary social standards (including childhood development delay) because social standards are defined by consensus. The same goes for specific example behaviors.

  • Delays in reaching, or failure to achieve milestones in motor skills development (sitting, crawling, walking)
  • Slowness learning to talk, or continued difficulties with speech and language skills after starting to talk
  • Difficulty with self-help and self-care skills (e.g., getting dressed, washing, and feeding themselves)
  • Poor planning or problem-solving abilities
  • Behavioral and social problems
  • Failure to grow intellectually, or continued infant childlike behavior
  • Problems keeping up in school
  • Failure to adapt or adjust to new situations
  • Difficulty understanding and following social rules

We can bucket the remaining traits into three broad categories.

All three buckets contribute to intellectual stagnation. The intellectual gap between high versus low IQ people widens as they age.


[1] For reference, 130 ($+2\sigma$) is an average undergraduate mathematics major and 103 ($+0.2\sigma$) is an average undergraduate major in social work[source].

[2] My list of symptoms comes from this article on Wikipedia, retrieved July 24, 2020.