Table 2.

Descriptive statistics and difference scores^* of self-reported age at menarche in a longitudinal study of 253 adolescent girls

	Total M (SD)	Age 11 M (SD)	Age 13 M (SD)	Age 15 M (SD)	Age 17 M (SD)
n	253	43	52	87	71
Age at Menarche First Report	12.40 (1.25)	12.20 (0.94)a	12.44 (1.11)a	12.37 (1.22)a	12.53 (1.52)a
In-person Interview Mean Age at Menarche	12.43 (1.17)	12.15 (.89)a	12.53 (1.07)a	12.40 (1.14)a	12.55 (1.38)a
Phone Interview Mean Age at Menarche	12.19 (1.30)	12.10 (1.02)a	12.05 (1.36)a	12.12 (1.25)a	12.42 (1.46)a
In-Person Interview Mean – Phone Interview Mean	0.52 (0.50)	0.29 (0.37)a,b	0.55 (0.53)a	0.61 (0.55)a,b	0.51 (0.44)b
Average difference (years): In-person & phone *	2.33 (2.20)	1.39 (2.40)a	2.57 (2.55)b	2.60 (2.23)b	2.39 (1.57)b
Average difference (years): In-person interview only*	0.58 (0.74)	0.28 (0.42)a	0.62 (0.63)a	0.66 (0.72)a	0.61 (0.94)a
Average difference (years): Phone interview only*	2.16 (1.58)	1.31 (2.41)a	2.33 (2.57)b	2.45 (2.28)b	2.16 (1.55)b

Note.

^*Difference scores represent discrepancy estimates calculated as the difference between the maximum reported age at menarche and minimum reported age at menarche across all assessments (in-person and phone), across in-person interviews only, and across phone interviews only. Means in same row not sharing superscripts (a, b, c) differ at p < .001 in the Bonferroni significant difference comparison. Annual in-person interviews were conducted three times and phone interviews were conducted quarterly (i.e, 3, 6, and 9 months; 9 total) after each annual visit.