<p>The author is simply not being explicit. The </p>

<blockquote>
  <p>correlation</p>
</blockquote>

<p>is neither <em>r</em> or <em>r</em><sup>2</sup>, it is simply the relation between x and y.</p>

<p><a href="https://en.wikipedia.org/wiki/Pearson_correlation_coefficient" rel="nofollow noreferrer">Pearson's correlation coefficient, or <em>r</em></a> 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.</p>

<p>The <a href="https://www.sciencedirect.com/topics/mathematics/coefficient-of-determination-r2" rel="nofollow noreferrer">coefficient of determination, or <em>r</em><sup>2</sup></a> 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 <em>r</em><sup>2</sup> near 0 indicates that little of the variation is explained by the different input values.   </p>

<p>Now to your book; 70% seems indeed like a lot. I thought it was approximately 40% and this is backed up by <a href="https://ghr.nlm.nih.gov/primer/traits/intelligence" rel="nofollow noreferrer">NIH</a> and <a href="https://www.scientificamerican.com/article/is-intelligence-hereditary/" rel="nofollow noreferrer">Scientific American</a> that mention approximately 50%. However <a href="https://en.wikipedia.org/wiki/Heritability_of_IQ" rel="nofollow noreferrer">wikipedia</a> mentions numbers up to 86% and back this statement up with influential articles. <a href="https://www.nature.com/articles/mp2014105" rel="nofollow noreferrer">(Plomin &amp; Deary, 2015)</a> indeed postulate that </p>

<blockquote>
  <p>The heritability of intelligence increases from about 20% in infancy to perhaps 80% in later adulthood.</p>
</blockquote>

<p><sub><strong>Reference</strong><br>
<strong>-</strong> <a href="https://ghr.nlm.nih.gov/primer/traits/intelligence" rel="nofollow noreferrer">Plomin &amp; Deary, <em>Molecular Psychiatry</em> (2015); <strong>20</strong>: 98–108</a></sub></p>

CC BY-SA 4.0
2019-09-23T17:17:25.777Z
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?
toljoas
CC BY-SA 4.0
2019-09-23T17:46:55.907Z
@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'.
AliceD
CC BY-SA 4.0
2019-09-23T14:05:41.613Z
2019-09-23T14:27:29.080Z
2019-09-23T14:27:29.080Z
AliceD
<p>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): </p>

<blockquote>
  <p>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.</p>
</blockquote>

<p>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!).</p>

<measurement><methodology><statistics><iq><correlation>
Correlation used as explanatory device in ''The neuroscience of Intelligence'
toljoas
# Correlation used as explanatory device in ''The neuroscience of Intelligence'

(Asked by: username_0 on 2019-09-23)

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!).

**Tags:** measurement, methodology, statistics, iq, correlation


---

## 1 answers

### Answer by username_1 on 2019-09-23. Score: 1 | Accepted answer

The author is simply not being explicit. The

> correlation

is neither *r* or *r*2, it is simply the relation between x and y.

[Pearson's correlation coefficient, or *r*](https://en.wikipedia.org/wiki/Pearson_correlation_coefficient) 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 *r*2](https://www.sciencedirect.com/topics/mathematics/coefficient-of-determination-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 *r*2 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](https://ghr.nlm.nih.gov/primer/traits/intelligence) and [Scientific American](https://www.scientificamerican.com/article/is-intelligence-hereditary/) that mention approximately 50%. However [wikipedia](https://en.wikipedia.org/wiki/Heritability_of_IQ) mentions numbers up to 86% and back this statement up with influential articles. [(Plomin & Deary, 2015)](https://www.nature.com/articles/mp2014105) 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](https://ghr.nlm.nih.gov/primer/traits/intelligence)

> **Comments:**
> **username_0**: 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?  
> **username_1**: @username_0 - 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'.  

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