Let's make it "relative"

 

In the last few days, with the observed incidence's continuous increase, we witness a "confrontation" competition. There is a strong need among journalists and commentators to reference the first phase of the epidemic to relate what we are observing today. In many televised debates, comparisons between absolute numbers are presented, which, in general, make very little sense. These comparisons try to relate the current phase with the critical stage of the highs of late March and early April. In our opinion (and not only ours), this attempted comparison is not valid at all. In the first phase of the epidemic, cases of positive SARS-Cov-2 were intercepted through "diagnosis." In contrast, today, they are mainly found through "screening" and tracing.

Comparisons must always be made in relative terms, where the adjective "relative" is used to indicate that the quantities to be compared must be considered in "relation" (related) to the procedure from which they are derived. For example, comparing cases of COVID-19 only makes sense if these refer to the number of tampons used. But not all swabs, only those used to find new cases (the situation where 1 swab = 1 person). This is to check the differences between a diagnostic and a screening strategy.

The need to analyze relative data, or relationships between connected quantities, such as odds, proportions, rates, risks, odds, and all further processing, has always been a central theme of our posts and public interventions. In this sense, if we want to find some connection between the first wave and the current phase, we should start from the relationship between positive cases observed and swabs carried out.

In the graph, we reported this relationship, relative to the total swabs (in red) and the swabs for test only (in blue, excluding the control swabs to verify negativization to the virus). Recall that the data reported only the total swabs in the first phase of the epidemic, with no separation between test swabs and control swabs. The "red" ratio, although not correct from a statistical point of view, is still informative of the trend of the epidemic. It represents a lower limit to the "blue" ratio, which estimates the "positive rate."

Analyzing these two relationships' dynamics, the only similarity that can be guessed is between the initial phase of late February-early March and the current one. This seems to indicate that we are at the beginning of a second phase. Therefore any comparison with the maxima of the first wave is really inconsistent on a statistical level.

We are then in an initial phase of acceleration of the infection, but still manageable. Some restrictive measures can be though for specific commercial or leisure activities. Yet, they are far more sustainable than a new generalized closure (which may be the only "final weapon" if this rise does not stop). After all, in general, to citizens, it is required very little: wear a mask, respect the physical distance, wash your hands often. We can do it. Just try seriously.