program define chisq4
    version 4.0

    preserve
    clear
    gph open
    gph pen 1

    set obs 501

    gen x=70*uniform()
    gen y=.1*uniform()
    graph y x,xlab(0,10,20,30,40,50,60,70) ylab(0,.025,.05,.075,.1) s(i)
    gphconv

    replace x=70*((_n-1)/500)

    pdf_chi2 x y 10
    lines x y

    pdf_chi2 x y 20
    lines x y

    pdf_chi2 x y 30
    lines x y

    pdf_chi2 x y 40
    lines x y

    gph text 1000 16000 0 0 chi-square curves for 10, 20, 30, and 40 degrees of freedom

    gph close

    restore
exit
end