File:IQ curve.svg

%standard deviation:
sigma = 15;

%IQ values:
IQ=55.5:144.5;

%Gaussian function:
G=exp(-(IQ-100).^2./(2*sigma^2));
H=exp(-(IQ-100).^2./(2*sigma^2));

%Normalisation in the [0:100] range
G=100*G/sum(G);
H=100*H/sum(H);

%to plot them in different colors
G(1:15)=0;
G(31:45)=0;
G(61:75)=0;

H(16:30)=0;
H(46:60)=0;
H(76:90)=0;

%output to text file:
T=[IQ; G; H];
T = T';
save -ascii 'IQ_curve.dat' T;

A symmetric plot was desired, therefore the domain was shifted by 0.5. It saves the samples in an external file called IQ_curve.dat. To get the plot in different colours, the function is split in two different functions: when one is zero the other one is non-null and vice versa. Plotting G and H will get the effect desired. In order to get the SVG, the following Gnuplot code was used:

set terminal svg
set output "IQ_curve.svg"
set xrange [55.5:144.5]
set key off
set xzeroaxis linetype -1 linewidth 0.5
set yzeroaxis linetype -1 linewidth 0.5
set xtics axis
set ytics axis
plot "IQ_curve.dat" using 1:2 with impulses linewidth 1.5, \
     "IQ_curve.dat" using 1:3 with impulses linewidth 1.5

Then I post-processed the file with Inkscape.

1. ↑ Kaufman, A.S. (2009(2009)). IQ Testing 101. New York (NY): Springer Publishing. pp. 104-109. ISBN 978-0-8261-0629-2 .