Table S4.

Mean scores and results of between- and within-family analyses (NLSY participants)

	Sibship size	Between-family									Within-family
		n	Observed mean scores by birth-order position				Effect of sibship size		Effect of birth order		n	Estimated mean scores by birth-order position				Effect of birth order
			1	2	3	4	F	P	F	P		1	2	3	4	F	P
Extraversion	2	1,732	50.88	50.78					0.04	0.837	732	49.93	49.94			0.00	0.988
	3	1,026	50.12	51.06	49.63				1.56	0.212	819	49.45	49.17	50.18		0.49	0.612
	4	420	50.20	50.14	48.09	50.79			1.26	0.287	511	48.93	49.56	49.50	53.22	1.83	0.142
		3,178					1.03	0.358	1.50	0.212	2,062					1.88	0.131
Emotional stability	2	1,732	50.37	49.75					1.66	0.197	732	50.31	50.31			0.00	0.995
	3	1,026	50.14	51.42	50.16				1.56	0.211	819	50.43	49.31	49.11		0.97	0.380
	4	420	49.46	48.45	50.89	50.73			1.30	0.275	511	48.55	49.85	50.52	51.12	0.68	0.564
		3,178					1.17	0.311	0.43	0.729	2,062					0.12	0.946
“I see myself as: anxious, easily upset”	2	1,732	49.85	50.11					0.24	0.627	732	49.41	49.54			0.04	0.851
	3	1,026	50.54	48.71	49.61				0.31	0.734	819	49.85	50.79	50.82		0.66	0.518
	4	420	50.80	52.47	48.87	49.29			4.36	0.005	511	50.75	50.05	49.94	49.52	0.16	0.926
		3,178					2.95	0.053	2.53	0.055	2,062					0.14	0.936
Agreeableness	2	1,732	50.18	50.12					0.01	0.908	732	49.43	50.41			2.35	0.126
	3	1,026	49.81	50.48	50.67				0.80	0.451	819	50.53	50.38	49.46		0.46	0.631
	4	420	49.49	50.50	49.47	51.24			0.75	0.521	511	48.52	50.20	50.42	49.30	0.76	0.517
		3,178					0.29	0.751	0.77	0.512	2,062					0.90	0.442
Conscien-tiousness	2	1,732	50.01	50.05					0.01	0.927	732	49.74	49.71			0.00	0.971
	3	1,026	49.67	49.36	50.16				0.46	0.630	819	49.42	48.91	50.89		1.85	0.158
	4	420	51.53	50.24	47.92	49.03			2.41	0.067	511	51.16	51.64	49.45	50.34	0.94	0.423
		3,178					0.38	0.681	0.48	0.695	2,062					0.13	0.944
Openness to experience	2	1,732	50.48	50.14					0.53	0.465	732	50.30	50.51			0.09	0.758
	3	1,026	50.44	51.30	50.85				0.62	0.537	819	50.75	49.18	48.07		2.89	0.057
	4	420	49.65	49.53	49.41	50.05			0.07	0.977	511	48.84	49.76	49.45	51.90	0.86	0.464
		3,178					1.95	0.142	0.06	0.979	2,062					1.29	0.277
Intelligence (IQ)	2	1,634	100.79	98.76					7.69	0.006	896	100.94	98.38			17.84	<0.001
	3	925	99.01	96.42	97.25				2.56	0.078	954	99.87	98.05	96.37		4.68	0.010
	4	355	95.30	96.34	93.48	95.24			0.41	0.746	549	99.05	95.81	93.73	94.29	3.41	0.018
		2,914					11.49	<0.001	3.87	0.009	2,399					11.82	<0.001