I am wondering how "unique" I am with the following characteristics: red hair (now white), AB(-) blood type, left-handed, IQ of 130 and Ph.D degree in cell biology. I've found that left handedness in the general population is 7 - 10%, AB(-) blood type is 0.3% (4% for the total of AB -/+), but can't relate the remain characteristics and determine the probability of having all of the above characteristics. Can you help?
Redhair about 1-2% of the popuation. IQ of >130 and a PhD I would guess would be well under 1% and a PhD in cell biology well under 0.01%. The probability of having all of them (since there is no reason to think the various traits you mention are linked, other than IQ and having a PhD) is simple maths; just multiply each of the probabilities.
More generally it is important to remember we are all unique - even "identical twins" are not since environmental factors subtly alter us during development and as adults.
The traits mentioned are not all likely to be independent, so it isn't a simple multiplication of the probabilities. Apologies for the statistical pedantry, but there have been too many cases, especially in courtrooms, of this sort of argument that can be used to sway people into convicting people on dodgy evidence. This sort of problem needs a multivariate analysis.
And as this is a science site, IQ is a fairly slippery concept and has the unfortunate property that the more IQ tests you take, the higher you will score. Thus, to some extent, IQ tests measure how good you are at taking IQ tests. Steve J. Gould's book 'The Mismeaure of Man' is an excellent introduction to this issue. I am not saying that intelligence is not heritable, just that IQ is not the way to measure it.
Thanks and agreed re IQ measurement it should also be noted that perfomance in these tests varies between ethnic groups. Not because of differences in intelligence but because of the way the questions are structured/phrased and people's perception of the questions.
Am puzzled by your first statement: "The traits mentioned are not all likely to be independent."
Which of hair colour, blood type, left-handedness and intelligence do you think may be dependent on each other?
More from Jon via an e-mail to the site:
"Thanks for your quick reply to my question regarding how unique my characteristics are. I must admit I considered and agree with both of your comments. I considered a simple arithmetic answer, but think a multivariant analysis is required to address this question. Also, taking IQ tests is not the best measurement of a persons intelligence; one "learns" how to take tests. From what I've read, there appears to be a correlation between left handedness and the very upper (>140) and very lower IQ (
Hi Dave W , Dave H and Jon,
Jon, firstly thanks for writing back. We get relatively little feedback from people as to whether our answers have helped.
Your points about left-handness and intelligence have a bimodal distribution in the IQ scores were one source of possible non-independence. And having a Ph. D. and a high IQ are likely to be correlated. However both of these could be down to environmental factors. I have two left-handed parents, one of whom was stopped from using their left-hand at school, the other was left alone. And being male also predisposes you to a more bimodal distribution.
If you are an Irish or Scottish Ryan, then red-hair becomes much more probable, although given the low incidence of AB- blood type in human populations I am happy to concede that any link between your blood type and hair colour is probably independent, but your chances of being red-haired if some of your genetic make-up is Scots or Irish are much greater than for the whole world population. The sample population can make a big difference.
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