I'm a newcomer to understanding and calculating heritability and
related statistics. I notice that heritability is a
variance-explained statistic (variance attributed to inheritance
divided by total between-subject variance). In the sphere of
experimental research, variance explained conveys a false impression
of the magnitude of an effect. You have to take the square root of
the variance explained to convert it to a correlation coefficient,
then interpret it using Cohen's scale of effect magnitudes (<0.1 =
trivial, 0.1-0.3 = small, 0.3-0.5 = moderate, >0.5 = large). Thus, a
variance explained of 0.01 (1%) is actually a small but non-trivial
effect, because it is equivalent to an effect size of 0.1.
So my question is this: should we take the square root of
heritability to get an idea of the contribution of inheritance to a
particular trait?
Supplementary question: can someone supply a definition of the
calculation of heritability in twin studies where you have
dizygotomous twins separated at birth acting as a kind of control for
monozygotomous twins separated at birth? The paper I am trying to
understand is Fox et al. (1996). There is disappointingly
insufficient detail in the Methods, and they refer to a text book
that I can't access. I've clicked around the web without success
looking for an approachable explanation. I'd really appreciate a
link to a good website on this topic.
Fox PW, Hershberger SL, Bouchard TJ (1996). Genetic and environmental
contributions to the acquisition of a motor skill. Nature 384, 356-358
Will
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Will G Hopkins, PhD FACSM
University of Otago, Dunedin NZ
Sportscience: http://sportsci.org
A New View of Statistics: http://newstats.org
Sportscience Mail List: http://sportsci.org/forum
ACSM Stats Mail List: http://sportsci.org/acsmstats
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