2
$\begingroup$

I am currently reading Dr. Richard Haier's book The Neuroscience of Intelligence. I have a base knowledge of statistics, but I am confused about the following extract from page 80 (chapter 2.4):

When correlations are computed in identical twins reared apart, the correlation is also one way to estimate heritability, so a correlation of .70 indicates that 70% of the variance in intelligence is due to genetic factors and 30% is not.

Is using correlation a valid way to estimate the heritability of a specific trait? I was under the impression that for a comparison of shared variance r² would have to be used, which would mean IQ is not 70% inherited, but only 49% (a huge difference!).

$\endgroup$
1
$\begingroup$

The author is simply not being explicit. The

correlation

is neither r or r2, it is simply the relation between x and y.

Pearson's correlation coefficient, or r is a measure of the linear correlation between two variables. It's value is between +1 and −1, 1 being a total positive linear correlation, 0 means no linear correlation, and −1 is total negative linear correlation.

The coefficient of determination, or r2 has a value between 0 and 1. A value near 1 indeed indicates that most of the variation of the response data is explained by the different input values, whereas a value of r2 near 0 indicates that little of the variation is explained by the different input values.

Now to your book; 70% seems indeed like a lot. I thought it was approximately 40% and this is backed up by NIH and Scientific American that mention approximately 50%. However wikipedia mentions numbers up to 86% and back this statement up with influential articles. (Plomin & Deary, 2015) indeed postulate that

The heritability of intelligence increases from about 20% in infancy to perhaps 80% in later adulthood.

Reference
- Plomin & Deary, Molecular Psychiatry (2015); 20: 98–108

$\endgroup$
  • $\begingroup$ Ah okay, so he used 'correlation' not as a statistical term, but as a therm for expressing that there is an association between the variables? $\endgroup$ – toljoas Sep 23 at 17:17
  • $\begingroup$ @toljoas - I reckon; I don't know the book, but from the context you can deduce what he means; if he isn't talking about p values, but only holds a monologue in popular scientific terms, he just means 'relation between x and y'. $\endgroup$ – AliceD Sep 23 at 17:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.