function p=emphys(x,y,z)

% x= severity of emphysema (0= no emphysema, 1= mild emphysema, etc.)
% y= sex (0= female, 1= male)
% z= # cigarettes smoked per day

lambda= 0.002 + 0.002*y + 0.05*z;
norm= 1 + lambda + lambda^2/2 + lambda^3/6 + lambda^4/24;
p= lambda^x/(norm * prod(1:x));
