Table 2.

Parameters that Depend on the Sexual Activity Group of Individuals

Parameter For Activity Group $i$	Activity Group
	Very Low	Fairly Low	Fairly High	Very High
% in specific activity groupa	45.1	36.4	17.7	0.7
Rate of forming main regular partnerships per ya (${\alpha }_{Mi})$	0.1	0.2	0.7	0.7
Number of sex contacts per main regular partner per d ($u_i$)	0.03	0.06	0.14	0.14
% with main regular partnera ($q_i$)	60	51	54	42
Number of casual partners per da (${\alpha }_{ci})$	0.006	0.044	0.139	0.7–1.0

^aParameters estimated from data from the first round of the “COVID-19, Sex, and Intimacy Survey” [25]. We used only data from the questions relating to sexual activity in the second half of 2019 (before the start of the pandemic in the Netherlands). Men in the very high sexual activity group reported more than 100 partners in the second half of 2019.