TABLE 4.

Percentage of bias in covariates between intervention and control groups in unmatched and matched samples of children in the 2003–2005 follow-up of the Hyderabad Nutrition Trial¹

			Bias after matching
	Bias in unmatched data	P value of bias	School enrollment	Schooling grade completed	Academic performance
Age	4.5	0.46	−2.5	−2.6	6.7
Birth order	−10.2	0.09	7.4	2.6	−0.4
Male child	−1.2	0.84	1.9	3	−0.8
Scheduled caste/scheduled tribe	19.9	0.001	−9.6	−9.2	0.4
Other backward caste	−16.7	0.006	5.5	1.7	−3.4
Non-Hindu household	−12.1	0.042	−4.7	−0.8	2.9
Wealth quintile 2	1.8	0.77	−1.8	0.5	2.5
Wealth quintile 3	0.2	0.98	−2.7	−8.6	−2.7
Wealth quintile 4	−3.2	0.59	8.2	7.1	−6.6
Wealth quintile 5	10.3	0.09	3.8	8.2	6.7
Father literate2	5.6	0.36	13.1	2.3	4.4
Father’s education: primary	−11.4	0.06	−1.9	0	4.4
Father’s education: secondary and above	−8.8	0.15	2.5	6.7	2.2
Mother literate	2.7	0.66	6.5	7.4	2.6
Mother’s education: primary and above3	−10.8	0.07	−2.00	5.4	8.6
Mean bias	8.0		5.0	4.4	3.7
Pseudo-R2	0.023		0.010	0.007	0.006
P-value for χ2	0.003		0.36	0.68	0.90

¹Values are %, unless stated otherwise. Bias is the percentage difference in the mean value of the variable in the intervention sample from that of the control sample. Matching was on propensity scores, using a one-to-one nearest-neighbor match with replacement within a radius of 0.01.

²“Father literate” had a statistically significant bias even after matching (13.1% bias, P < 0.05) in the analysis of enrollment.

³“Mother’s education: primary and above” had a statistically significant bias even after matching (8.6% bias, P < 0.1) in the analysis of academic performance.