What color are we today? It is the question we ask the first person we see every morning. As in the children's game "witch commands color," we stopped asking ourselves the reason for the choice of color, almost resigned. We talked about 21 indicators, designed and built to decide what we can and cannot do. Too many, redundant, and based on too old data to provide a timely response in an emergency. We discovered what Rt was and that a few decimals of Rt are precious to remain "yellow" and not pass "orange." As if there was only one way to estimate Rt. As if fixing the generation time needed to estimate Rt at the estimated values for Lombardy in February made some logical sense. Rt, like the North Star of Italian epidemiology. Perhaps the only thing that everyone knows how to calculate given there is EpiEstim in R that does it for us.
In our opinion, decisions are best made on observed and updated data. Remember that data heterogeneity is already considerable (public data are anything but "clean"). Then why make everything even more uncertain by estimating values whose reliability we do not know?
Suppose our aim is to block an area when the pressure on the health system is potentially unsustainable. In that case, we must use indicators that take it into account and indicators that allow us to understand the infection's state. There are many ways to follow, but we have been taught that we must start from simple things and, if not sufficient, move towards more complex approaches.
So let's start from here: not just one indicator but two. For example, let's take the weekly incidence (on the population residing in a region) and the average employment of the weekly intensive care units compared to the number of beds. With these two indicators on a graph, establishing, as an example, the two thresholds (30% for intensive care and 250 infections per 100 thousand inhabitants) already used by the government or proposed by the CTS, we obtain what is shown in the graph: Marche, Friuli, Trentino and Veneto in the red zone, 5 regions in the orange zone and the rest yellow.
It must be said that the situation is complicated. For example, Calabria carries out less than 1500 swabs per week per thousand inhabitants, bringing up the country's rear. It seems that it does not carry out surveillance activities. Maybe two indicators based on observed data are not enough, but at least we know exactly why we are yellow today and orange tomorrow.