Current IQ tests typically have standard scores such that the mean score is 100 with each standard deviation from the mean counting for 15 IQ points.[1] The plot shows, assuming that such scores have a normal distribution, the percentage of people getting a score versus the score itself, from 55 to 145 IQ, that is over a span of six standard deviations. Spans are represented with different colors for each standard deviation above or below the mean. The plot was created with the following gnuplot code:
setterminalsvgname'IQ_curve'size600,480font',10'roundedsetoutput'IQ_curve.svg'mu=100.0sigma=15.0from=55to=145# Normal distribution:# (continuos normalization approximation, good to ~10 digits in this case)P(x)=exp(-(x-mu)**2/(2*sigma**2))/(sqrt(2*pi)*sigma)*100# By sigma intervals:oddsi(x)=(int(abs(x-mu)/sigma)%2)^(x<mu)Pm(x)=(x==mu)?P(x):1/0# sample at muPo(x)=(oddsi(x)&&(x!=mu))?P(x):1/0# samples in odd sigma intervalsPe(x)=(!oddsi(x)&&(x!=mu))?P(x):1/0# samples in even sigma intervalssetkeyoffsetborder3setxlabel'IQ'setxtics10outnomirrorsetmxtics2setylabel'Population, %'setytics1outnomirrorsetmytics2setsamples(to-from+1)setstylefunctionimpulsesplot[x=from:to]\
Pm(x)lw2,\
Po(x)lw2,\
Pe(x)lw2
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