Table A1.

Friendship Selection Table by Gender and Sexual Debut Status

Boys			Girls
Ego	Alter		Ego	Alter
	Debuted	Not debuted		Debuted	Not debuted
Debuted	0.399	0.280	Debuted	0.228	0.071
Not debuted	0.379	0.348	Not debuted	0.174	0.329

Note. This table shows the net effects of sexual debut status of ego (nominator) and alter (nominee) on friendship network formation (Table 2) by gender and gives the model-predicted propensities of friend selection among same-gender friends. In this table, the ego in rows sends a tie to the alter in columns; hence, it allows us to go beyond the marginal effects in Table 2 and thereby examine the prevalence of concordant pairs over discordant pairs based on sexual debut. The propensities to form sexually homophilous pairs are expressed in the diagonals, and comparisons between the diagonal values and the off-diagonal values indicate the degree of assortative selection based on sexual debut. Comparison of the diagonal and off-diagonal values for girls and boys confirm that sexual homophily is more prevalent for the former than the latter. Assuming other attributes and network characteristics are identical, the log-odds ratio for the debuted boys to select other debuted boys relative to nondebuted boys (0.399 – 0.280 = 0.119) was lower than the debuted girls’ log-odds selection of other debuted girls over nondebuted girls (0.228 – 0.071 = 0.157). Similarly, the nondebuted boys’ log-odds ratio to choose other nondebuted boys over the debuted ones was – 0.031 (= 0.348 – 0.379), which was also lower than nondebuted girls’ log-odds ratio of befriending other nondebuted girls over debuted girls (0.329 – 0.174 = 0.155). Therefore, we found support for our hypothesis that girls’ tendencies toward sexual homophily are stronger than boys’.