Table 5.

Functional Form of Backward Digit Span in the ECLS-K:2011 and Restricted-range PSID-CDS.

PSID-CDS, Backward Digit Span						ECLS-K:2011, Numbers Reversed
Functional Form		Model 1	Model 2	Model 3	Model 4	Model 1	Model 2	Model 3	Model 4
Linear	b	0.620	2.360	5.577		7.307	18.051	38.796
	SE	0.023	0.280	2.529		0.053	0.196	0.551
	Lower CI	0.575	1.810	0.619		7.203	17.666	37.711
	Upper CI	0.664	2.909	10.534		7.410	18.435	39.880
	p-value	<.001	<.001	0.027		<.001	<.001	<.001
	AIC	105055483				351071978
	BIC	105055507				351072019
Quadratic	b		−0.101	−0.488			−1.461	−8.266
	SE		0.016	0.305			0.027	0.170
	Lower CI		−0.134	−1.086			−1.514	−8.602
	Upper CI		−0.069	0.110			−1.408	−7.930
	p-value		<.001	0.110			<.001	<.001
	AIC		104487838				349613642
	BIC		104487868				349613692
Cubic	b			0.015				0.605
	SE			0.012				0.015
	Lower CI			−0.008				0.576
	Upper CI			0.039				0.635
	p-value			0.208				<.001
	AIC			104463551				348801730
	BIC			104463586				348801784
Logarithmic	b				5.250				20.714
	SE				0.186				0.126
	Lower CI				4.886				20.466
	Upper CI				5.615				20.962
	p-value				<.001				<.001
	AIC				104704659				348702742
	BIC				104704683				348702778

Note: The age range for the PSID-CDS is restricted to ages 6–11 to mirror the ages in the ECLS-K:2011. Missing data were handled using multiple imputation, and baseline cross-sectional sampling weights were used. Bolded values indicate best fitting models.