Table 6:

Performance of competing methods to impute missing Hg data at 19 months and at 19 years among SCDS Main Cohort participants, based on a comparison of imputed values to observed Hg values. For each method, table entries show mean differences, sum of squared (SS) differences, and the ratio of the mean differences (in absolute value) and SS differences to the average Z-score method. Comparisons are based on the subset of n = 621 participants in early childhood and n = 379 in early adulthood who have complete Hg data at all ages within the time window.

	Average Z-score	Average	Geometric average	AUC	Average Z-score*	FCS-9 single*	FCS-9 mean*	FCS-4 mean*
19 months
Mean difference	−0.50	1.64	1.24	1.60	−0.38	0.25	−0.72	−0.79
SS differences	6278	9378	8016	8717	6337	10,068	5705	5564
Mean ratio†	–	3.30	2.50	3.22	–	0.65	1.90	2.08
SS ratio†	–	1.48	1.26	1.38	–	1.59	0.90	0.88
19 years
Mean difference	−0.65	−4.31	−4.96	−4.16	−0.56	0.25	−1.01	−1.07
SS differences	10,004	16,142	18,572	16,109	10,419	18,945	10,415	10,314
Mean ratio†	–	6.60	7.59	6.37	–	0.44	1.78	1.87
SS ratio†	–	1.55	1.78	1.55	–	1.82	1.00	0.99

^*Imputation uses Hg data at the age of interest from 50% of the sample.

^†Denominator for ratio calculation is average Z-score; the mean ratio is an absolute value