st: generating random variables from logistic distribution

[Kit Baum <baum@bc.edu>]

Not clear to me either how so-called generalized logistic  
distribution relates to the garden variety one defined here. In any  
case here is a routine in the style of Hilbe that does the job, and a  
test of whether it appears to meet the specs (which it does for  
sufficiently large N):

capt program drop rndlog

*!version 1.0 04aug2005 CFBaum
* following syntax of J. Hilbe rnd package
* logistic distribution random number generator
* per David Harrison msg to Statalist 04aug2005
* Example: rndlog 1000 0 .5  [set obs 1000; 0 = mean; .5 = b]

program define rndlog
        version 3.1
*        set type double
        cap drop xlogistic
        qui     {
                local cases `1'
                set obs `cases'
                mac shift
                local mn `1'
                mac shift
                local b `1'
                mac shift
                tempvar ran1
                noi di in gr "( Generating " _c
                gen double `ran1' = `mn' - `b'*log(1/uniform() - 1)
                gen double xlog = `ran1'
                noi di in gr "." _c
                noi di in gr " )"
                noi di in bl "Variable " in ye "xlog " in bl "created."
                lab var xlog "Logistic random variable"
*                set type float
       }
end

clear

scalar mu=5
scalar b=3
rndlog 100000 mu b
su xlog,detail
assert reldif(r(mean),mu) < 0.01
assert reldif(r(Var),1/3*_pi^2*b^2) < 0.01
assert reldif(r(skewness),0) < 0.1
assert reldif(r(kurtosis)-3.0,6/5) < 0.1


Kit Baum, Boston College Economics
http://ideas.repec.org/e/pba1.html


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