KNOWLEDGEBASE - ARTICLE #2174
Equations for normal and lognormal distributions
Prism has built-in equations for normal (Gaussian) and lognormal distributions. But these are not quite in synch, so it is hard to graph both so they have the same area under the curve (AUC).
Here are equations that create distributions with an AUC of 1.0.
Normal (Gaussian)
Two parameters: Mean and SD
Y=1/(SD*sqrt(2*pi))*exp(-0.5*((X-Mean)/SD)^2)
Lognormal
Two parameters: GeoMean and GeoSD
s=ln(GeoSD)
m=ln(GeoMean)
Y=(1/X)*(1/(s*sqrt(2 * pi))) * exp(-1* (ln(X)-m)^2/(2*s^2) )
m=ln(GeoMean)
Y=(1/X)*(1/(s*sqrt(2 * pi))) * exp(-1* (ln(X)-m)^2/(2*s^2) )