Table 1.

Comparison between R and RI indexes.

Italy						Lombardia region					Italy—without Lombardia region
Field	Time window		RI	σ/RI	Rt	Field	Time window	RI	σ/RI	Rt	Field	Time window	RI	σ/RI	Rt
T0–T1	February 24–March 13		0.11	1.24	1.12	T0–T1	February 24–March 31	0.34	4.01	1.40	T0–T1	February 24–March 22	0.03	0.43	1.26
T1–T2	March 14–April 6		0.30	0.73	0.94	T1–T2	Aril 1–May 3	1.10	2.05	1.01	T1–T2	March 23–April 6	0.24	0.57	0.99
T2–T3	7 April–19 April		2.21	0.81	0.94	T2–T3	May 4–August 18	− 1.71	2.59	1.14	T2–T3	April 7–April 19	6.07	1.65	0.98
T3–T4	April 20–July 24		− 2.60	1.15	1.03	> T3	> August 19	1.31	3.59	1.11	T3–T4	April 20–July 10	− 1.16	4.99	0.94
> T4	> July 25		0.89	2.28	1.05						> T4	> July 10	0.78	4.22	1.07

This table compares RI and Rt, within the time windows (Tn-Tn-1), defined for the three cases examined: Italy, Lombardy and Italy without Lombardy. It clearly emerges that the RI index records the acceleration and deceleration of the epidemic curve, both over time and in the different areas of the examined Italian territory. In the first phase, this acceleration seems to be connected to the initial imbalance between the newly infected and the healed, with an increase in the number of infected but with a reduced increase in the healed. In this case RI assumes low values close to zero. In the same phase, however, the R (t), while recording high values of the new positives, does not show the rapid evolution of the healed, as happens with RI, which assumes increasing values assuming values > 1. The fast evolution of the pandemic curve, with a rapid reduction of the new infected, is denounced by the values by RI, which assumes values < 0. In the later stages, the recovered play a dominant role and, therefore, the RI index drastically increases while Rt decreases due to the overcoming of the epidemic peak. The phases following the peak are described by the two indices in a different way as Rt remains substantially stable but RI shows a greater sensitivity to changes in the infected.