[joshocar]

As far as I understand it R is not a rate because it does not include time. Diseases that take on average a few days for you to pass on verses a few months will have different growth rates. For example, an STI might have an R factor of 3, but the rate is completely dependent on how often people have unprotected sex.

[scoot]

Good point, R is often referred to as a rate both in media and academic publications, but "number" or "value" appears to be more correct. Fixed.