# What am I doing wrong in calculating R0 using Next Generation Matrix?

I have been trying to calculate $$R_0$$ (using Next Generation Matrix) for the following model from a published paper (see the screenshot below). I am getting an expression for $$R_0$$ that is very similar to theirs, the only difference is that I have $$S_hS_m$$ appearing in the numerator which they do not have. My transition and transmission matrices are 2 by 2 in size and they come from the equations for $$I_{hd}$$ and $$I_{md}$$. It is not just this paper but I am experiencing the same thing with some other models too so I am sure I am making a mistake in the procedure somewhere, but no idea where.

• It would be helpful if you included your own work in the question as well, otherwise there isn't really any way to determine the error. – DMcMor Jul 22 at 16:20