I believe that this website offers a better analysis of IQ than you will find elsewhere online.
August, 2019, April 2025
My name is Davi A. May. I am retired, and have had the time and energy to spend day after day studying and analyzing the many areas of IQ science, without concern for making a career or a profit. The footnotes reference over 120 scientific articles, but I have read many more. These are ususally written with confusing technical terms. My motivation in starting this work was curiosity about certain current events. I wanted to see for myself how intelligence was passed from one generation to the next. And in creating this site I hope to allow you to see for yourself.
The insights of IQ science are important to understand our world.
The subject of IQ is often very emotional because many folks believe that individuals or groups should not be judged. Discussion of IQ, or even consideration, is often taboo, and can even engender hatred. Thus, in recent years, the results of IQ studies often remain buried in scientific journals. Many intelligence scientists will not write for the general public— for fear of endangering their jobs and alienating their friends. (Sources 1, 2). I must stress at the outset that to judge an individual, if one is going to judge, one should not use stereotypes or ignore the qualities of the whole person.
It has become accepted now, as it was years ago, that SATs or other tests that essentially measure intelligence are necessary . Recent experience eliminating SATs has shown that tests roughly equivalent to IQ tests lead to better outcomes for all concerned. Understanding the whys of IQ test score difference is import in judging the structure of society.
My Definitions for the factors affecting IQ
I avoid the confusing terms “nature”, “nurture” and “genes”. I use the terms heredity, environment, culture and chance. By heredity I mean influences that come from DNA and unchanging epigenetics.By environment I mean influences that are external to individuals and their cultures, such as iron anemia, air pollution, lead poisoning or school quality. By culture I mean influences in a family and the people with whom they associate. By chance I mean random events that modify sperm or eggs, the combination of chromosomes, or alter the environment in the womb.
Understanding the difference between the study of IQ in families and IQ in groups
The study of IQ is about differences in IQ between individuals and between groups. A person takes an IQ test and that is their IQ. Nothing we know today, and probably nothing that we ever will know, will allow us to predict exactly or closely one persons IQ. What we try to learn is what makes one person do better than another on IQ tests. Is it due to their family inheritance — heredity; or is it due to their environment; or just chance? Chance has mainly been ignored in most studies, but it is very important..
Very Elemental Statistics for studying IQ
To understand this website, you must know the meaning of the terms “correlation” and “variance explained”.
Both terms apply to groups of people, not to individuals. You must have a set of data for a group. The greater the amount of data the more accurate will be the correlations and variances explained. The studies mentioned on this website are large enough to give quite accurate data.
A correlation of 1 or 100% between two measures of a group means that if you know one value about an individual in the group you can predict exactly the other value for that individual. If the correlation is somewhat close to 100%, your prediction will be somewhat close to its actual value. For example, because IQ tests correlate highly with Scholastic Aptitude Tests (SATs) and ACTs (Source 3) and success in intellectual professions, if an IQ test result is high, the results on SATs (and success in intellectual professions) are very likely to be superior. If you know a persons result on an IQ test you can predict quite accurately what their result will be if they take the test again.
A 0 correlation means that if you know one value for an individual you cannot predict whatsoever what the other value will be. A low correlation means that any prediction made might be pretty far off.
Correlation do not, in themselves, prove causality. For example, cancer does not increase the odds of cigarette smoking. It is the opposite. So whenever you want to prove that a correlation shows cause and effect, you must either have a mechanism, and you must try to eliminate, or control for, all other possible causes that might affect both elements of the correlation. All reputable scientific studies attempt to do this (but often fail). For example, you must compare the diets of cigarette smokers versus non-smokers.
You cannot add correlations together! To determine what effect a correlation has on an outcome, you must use a variance explained. A variance explained is a correlation times itself (its square). (The explanation requires a statistics course.) Thus, for example, if the correlation between two values is 0.8 (80%), the variance explained is 0.64 (= 0.8 x 0.8) = 0.64 ( 64%). If the correlation for lung cancer and cigarette smoking happened to be 40%, the amount of causality would be 16%; the rest might be genes or chance, or diet.
All of the individual variances explained affecting the outcome must add to 100%. For IQ test results, the variances explained of heredity, environment, culture and chance, when added together, must equal 100% (unless you would include interventions by God or influences from the zodiac).
In the balance of this website I will explain IQ tests, then examine in turn what is known about heredity (in three types of studies), environment, culture and chance, and finally look at IQ among groups.
Next page:https://iqscience.net/iq-defined-and-the-tests-explained/
- https://www.nytimes.com/1977/03/27/archives/new-light-on-black-iq.html Thomas Sowell ↩︎
- https://www.commentarymagazine.com/articles/the-bell-curve-by-richard-j-herrnstein-and-charles-murray/ Book review by Chester E. Finn ↩︎
- http://www.iapsych.com/iqmr/koening2008.pdf ACT and general cognitive ability, Koenig et al., Intelligence 2008 ↩︎