Hi everyone, just want to blog an entry on the difference between Reproduction vs Growth rate that are commonly used in media these days.
The reproduction rate (academically denoted as R) is the infectious potential of a disease, namely how many secondary cases will be created from a primary case. It is necessary to create the projections in the SIR model and also gives a sensing of how viral the virus is. However data can be skewed due to asymptomatic infections. Nonetheless the bottomline usefulness is it helps to calculate the rate of flow from S to I under the SIR model.
The growth rate (denoted as r) is the ratio of number of new cases in a week against the number of new cases in the previous week. It is the ratio that the SG government is watching these cases (coupled with ICU utilisation rate).
Why a week and not two weeks or ten days? No definite answer, it's just easier to catch sensing that way. And again it has its limitations mainly due to asymptomatic infections too.
So please pay attention to what the media if quoting especially if you read international reports. Not all countries are focusing on the same parameters during this period.