The effect of a sibling on the first-born child’s health: evidence from two-child families in China

Figures & data

Table 1. The descriptions of key variables for first-born children with or without a sibling.

Variable name	Without a sibling			Having a sibling			Difference
	N	Mean	Std. Dev.	N	Mean	Std. Dev.
HAZ (height-for-age z-score)	3981	−0.352	1.285	1898	−1.024	1.201	0.672***
Boy (1 = boy; 0 = girl)	3981	0.565	0.496	1898	0.450	0.498	0.115***
Age (year)	3981	7.089	2.891	1898	8.329	2.543	−1.240***
Hukou (1 = rural; 0 = urban)	3981	0.594	0.491	1898	0.858	0.349	−0.265***
Log of household income per capita	3981	8.653	1.056	1898	7.933	1.000	0.720***
Mother's age (year)	3981	31.785	5.000	1898	31.617	3.860	0.168*
Mother's BMI	3981	22.255	3.161	1898	22.071	3.163	0.184**
Mother's educational years (year)	3981	9.282	3.294	1898	6.957	3.279	2.325***
Carbohydrates (g):three-day average	4208	204.093	86.216	1926	263.628	100.882	−59.535***
Fat (g):three-day average	4208	52.158	33.631	1926	45.02	28.414	7.136***
Protein(g):three-day average	4208	48.010	27.919	1926	48.967	18.391	−0.957 ***
Dietary variety score: three-day average	2912	2.559	2.208	937	1.774	1.898	0.785***
Having medical insurance (1 = yes; 0 = no)	4450	0.500	0.5000	2084	0.309	0.496	0.191***
Children age <6: does physical exercise?	1133	0.553	1.332	173	0.428	1.04	0.125
Children age 6+: does physical exercise?	1987	0.424	1.021	873	0.260	0.778	0.164***

Notes: *, ** and *** represent significance at the 10%, 5% and 1% levels, respectively. Having a sibling means that the first-born child has a younger sibling at the time of survey.

Source: Authors’ calculations using data from the China Health and Nutrition Survey (1991–2015).

Table 2. Effect of having a sibling on the first-born child’s HAZ.

Variables		(2)
	(1) OLS	ERM		(3) OLS
		1st stage	2nd stage
	HAZ	Having a sibling	HAZ	HAZ
Having a sibling	−0.178***		−0.810***
	(0.0368)		(0.124)
IV		1.720***
		(0.0984)
age gap				0.0351***
				(0.0129)
Boy	0.0592**	−0.513***	−0.00985	0.0670
	(0.0294)	(0.0432)	(0.0334)	(0.0488)
Age	0.0423***	0.239***	0.0744***	0.0384***
	(0.00716)	(0.0117)	(0.0100)	(0.0132)
Hukou	−0.193***	0.502***	−0.0876*	−0.261***
	(0.0367)	(0.0596)	(0.0448)	(0.0708)
Log of household income per capita	0.0572***	−0.233***	0.0135	0.0900***
	(0.0185)	(0.0277)	(0.0206)	(0.0303)
Mother's age	−0.00214	−0.0614***	−0.0105**	−0.0150*
	(0.00428)	(0.00687)	(0.00464)	(0.00839)
Mother's BMI	0.0172***	0.0133*	0.0175***	0.0100
	(0.00498)	(0.00722)	(0.00504)	(0.00804)
Mother's years of education (year)	0.0517***	−0.0456***	0.0420***	0.0465***
	(0.00501)	(0.00753)	(0.00544)	(0.00804)
Constant	−1.994***	−0.00362	−1.331***	−1.154***
	(0.260)	(0.549)	(0.290)	(0.387)
Observations	5,879	5,808	5,808	1,898
Control of wave dummies	YES	YES	YES	YES
Control of province dummies	YES	YES	YES	YES
Durbin-Wu-Hausman stat.		16.398***
F-stat.		499.907***

Notes: *, ** and *** represent significance at the 10%, 5% and 1% levels, respectively. Robust standard errors are in parentheses. Having a sibling means that the first-born has a younger sibling at the time of the survey. The value of Durbin-Wu-Hausman stat. and F-stat. show no presence of weak IV. That the sample size in Column (1) is larger than that in Column (2) was caused by the missing of the instrument variable.

Source: Authors’ calculations using data from the China Health and Nutrition Survey (1991–2015).

Table 3. Impacts of having a sibling on the first-born child’s HAZ across the income distribution, age, gender, or Hukou.

	Panel A: Stratified by household income per capita (quintiles)
	Bottom 20th percentile	20th–40th percentile	40th–60th percentile	60th–80th percentile	Top 20th percentile
Having a sibling	−0.933**	−0.518	−0.495*	−0.764***	−0.721**
	(0.436)	(0.373)	(0.254)	(0.264)	(0.306)
Observations	1,014	1,195	1,310	1,295	994
	Panel B: Stratified by age
	2< =age < 6		6 <=age < 9		9< =age< =12
Having a sibling	−1.059***		−0.638***		−0.717***
	(0.299)		(0.224)		(0.131)
Observations	1,910		1,799		2,099
	Panel C: Stratified by gender
	Boy		Girl
Having a sibling	−0.796***		−0.760***
	(0.157)		(0.175)
Observations	3,068		2,740
	Panel D: Stratified by Hukou
	Rural		Urban
Having a sibling	−0.703***		−0.578**
	(0.156)		(0.270)
Observations	3,961		1,847

Notes: *, ** and *** represent significance at the 10%, 5% and 1% levels, respectively. Robust standard errors are in parentheses. The additional control here is the age of children, the age of the mother, the body mass index of the mother, the years of education of the mother, the household per-capita income (inflated 2015), as well as the fixed effects of province and wave. Having a sibling means that the first-born has a younger sibling at the time of the survey. All the results above are based on the IV estimation method. The value of Durbin-Wu-Hausman stat. and F-stat. show no presence of weak IV.

Source: Authors’ calculations using data from the China Health and Nutrition Survey (1991–2015).

Table 4. Impact of having a sibling on first-born child’s dietary pattern.

Variables	(1)	(2)	(3)	(4)
	ERM	ERM	ERM	ERM
	Dietary diversity score	Carbohydrates (g)	Fat (g)	Protein (g)
Having a sibling	−0.808***	34.83***	−13.01***	−1.855***
	(0.0853)	(4.631)	(2.347)	(0.389)
Boy	−0.0989***	20.19***	1.260	3.755***
	(0.0293)	(0.423)	(1.018)	(0.908)
Age	0.0492***	12.37***	3.445***	3.033***
	(0.00769)	(0.793)	(0.158)	(0.0933)
Hukou	−0.0782**	5.689***	−4.439***	−2.532***
	(0.0371)	(1.344)	(1.558)	(0.486)
Log of household income per capita	0.0539***	0.0437	3.185***	1.792***
	(0.0161)	(1.929)	(0.485)	(0.202)
Mother's age	−0.00491	0.961***	0.00174	0.0663
	(0.00393)	(0.311)	(0.134)	(0.0622)
Mother's BMI	−0.00387	−0.548***	−0.0159	0.111***
	(0.00445)	(0.197)	(0.161)	(0.0220)
Mother's years of education (year)	0.0171***	−2.225**	0.614***	0.371***
	(0.00536)	(0.950)	(0.188)	(0.134)
Constant	0.158	140.9***	−7.071	7.263***
	(0.252)	(22.27)	(5.743)	(2.074)
Observations	3,784	5,888	5,888	5,888
Control of wave dummies	YES	YES	YES	YES
Control of province dummies	YES	YES	YES	YES
Durbin-Wu-Hausman stat.	18.478***	68.909*	85.820*	361.71**
F-stat.	141.673***	55.895*	55.895*	55.895*

Notes: *, ** and *** represent significance at the 10%, 5% and 1% levels, respectively. Robust standard errors are in parentheses. Having a sibling means that the first-born has a younger sibling at the time of the survey. All the results above are based on the IV estimation method. The value of Durbin-Wu-Hausman stat. and F-stat. show no presence of weak IV.

Source: The data in column 1 is from 1997 to 2015 CHNS, while the data in columns 2–4 are from 1991 to 2015 CHNS.

Table 5. Impact of having a sibling on first-born child’s medical insurance and activity.

Variables	(1)	(2)	(3)
	ERM	ERM	ERM
	Medical insurance	Activity(Age < 6)	Activity(Age> =6)
Having a sibling	−1.135***	−0.0789	−0.824***
	(0.101)	(0.494)	(0.181)
Boy	−0.109***	0.0395	0.00823
	(0.0380)	(0.0806)	(0.0595)
Age	0.0615***	0.302***	0.123***
	(0.0103)	(0.0413)	(0.0176)
Hukou	0.217***	−0.305***	0.0724
	(0.0496)	(0.0948)	(0.0702)
Log of household income per capita	0.126***	0.146***	−0.0235
	(0.0227)	(0.0488)	(0.0295)
Mother's age	−0.00858	0.00137	−0.0102
	(0.00565)	(0.0122)	(0.00790)
Mother's BMI	0.0224***	−0.00508	−0.00753
	(0.00600)	(0.0117)	(0.00826)
Mother's years of education (year)	0.00819	0.0491***	0.0167
	(0.00657)	(0.0164)	(0.0107)
Constant	−1.979***	38.00*	−93.18***
	(0.353)	(19.89)	(10.25)
Observations	6,456	1,288	2,805
Control of wave dummies	YES	YES	YES
Control of province dummies	YES	YES	YES

Notes: *, ** and *** represent significance at the 10%, 5% and 1% levels, respectively. Robust standard errors are in parentheses. Having a sibling means that the first-born has a younger sibling at the time of the survey. All the results above are based on the IV estimation method. The value of Durbin-Wu-Hausman stat. and F-stat. show no presence of weak IV. Our physical activity analysis includes two different age groups (<6 or 6+ years) because CHNS questionnaires divide the sample into these two different age groups.

Source: Authors’ calculations using data from the China Health and Nutrition Survey (1991–2015).

Table 6. The estimation results of robustness check.

VARIABLES	(1)	(2)	(3)
	FE	ERM	ERM
	HAZ	WAZ	HAZ
Having a sibling	−0.0613*	−0.638***	–
	(0.00506)	(0.105)	–
Number of siblings	–	–	−0.566***
	–	–	(0.0884)
Boy	–	0.0975***	−0.0137
	–	(0.0331)	(0.0327)
Age	−0.438	−0.00937	0.0673***
	(0.269)	(0.0109)	(0.00909)
Hukou	–	−0.0865**	−0.115***
	–	(0.0437)	(0.0434)
Log of household income per capita	−0.00373**	0.0261	0.0245
	(0.000187)	(0.0211)	(0.0199)
Mother's age	−0.00661	−0.00923	−0.00893**
	(0.00776)	(0.00565)	(0.00439)
Mother's BMI	0.0227	0.0519***	0.0169***
	(0.0237)	(0.00631)	(0.00490)
Mother's years of education (year)	−0.0204	0.0309***	0.0420***
	(0.00671)	(0.00581)	(0.00508)
Constant	−2.582	−1.220***	−1.435***
	(1.097)	(0.313)	(0.287)
Observations	6,467	4,548	6,130
Number of idind	3514	–	–
R-squared	0.065	–	–
Control of wave dummies	YES	YES	YES
Control of province dummies	–	YES	YES
Durbin-Wu-Hausman stat.	–	6.168***	25.5189***
F-stat.	–	357.857***	722.743***

Notes: *, ** and *** represent significance at the 10%, 5% and 1% levels, respectively. Robust standard errors are in parentheses. In Column (1), we used a fixed-effects model to estimate the effect of having a younger sibling on a child's HAZ. In Column (2), we estimated the effect of having a younger sibling on a child’s WAZ. In Column (3), we estimated the effect of the number of siblings on a child's HAZ.

Source: Authors’ calculations using data from the China Health and Nutrition Survey (1991–2015).

Table 7. Impact of having a sibling on first-born child’s health: estimated by PSM.

	HAZ		WAZ
	kernel matching	Nearest neighbor matching	kernel matching	Nearest neighbor matching
ATT	−0.2578***	−0.2571***	−0.2784***	−0.2170***
Observations
Treated group	1,898		1,331
Untreated group	3,981		3,256

Notes: *, ** and *** represent significance at the 10%, 5% and 1% levels, respectively. The observed covariates are the age of children, the age of the mother, the body mass index of the mother, the years of education of the mother, the household per-capita income (inflated 2015), as well as province and wave. Two groups are identified: those children with a younger sibling (treated group) and those who do not have a younger sibling (untreated group).

Source: Authors’ calculations using data from the China Health and Nutrition Survey (1991–2015).