Table S10.

Mean scores and results of between and within-family analyses after restricting the analyses to families in which all age gaps between consecutive siblings were within the range of 18–60 mo (NLSY and SOEP 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	3,984	49.90	50.34					2.11	0.146	1,020	50.31	49.97			0.32	0.571
	3	1,325	49.94	50.31	50.99				1.40	0.247	510	49.91	48.72	48.38		0.76	0.470
	4	358	50.77	49.62	51.09	50.35			0.35	0.791	145	51.53	50.57	48.03	50.06	0.48	0.694
		5,667					0.04	0.959	1.65	0.175	1,675					0.81	0.487
Emotional stability	2	3,984	50.54	49.92					3.81	0.051	1,020	51.26	50.29			2.77	0.097
	3	1,325	49.93	49.33	49.50				0.16	0.853	510	49.96	49.42	50.34		0.32	0.724
	4	358	51.07	50.65	48.79	50.74			0.92	0.432	145	47.88	51.99	52.94	54.10	1.60	0.196
		5,667					1.25	0.287	1.75	0.154	1,675					0.88	0.452
Agreeableness	2	3,984	50.17	49.72					1.93	0.165	1,020	49.45	50.58			4.28	0.039
	3	1,325	51.00	50.40	50.73				0.29	0.748	510	51.25	50.10	51.38		0.96	0.384
	4	358	51.89	49.96	50.21	49.15			1.23	0.300	145	50.96	51.38	49.72	46.50	0.35	0.791
		5,667					3.10	0.045	1.62	0.182	1,675					0.86	0.459
Conscien-tiousness	2	3,984	49.81	49.79					0.00	0.966	1,020	49.84	49.84			0.00	0.997
	3	1,325	50.20	50.23	50.53				0.13	0.882	510	49.17	48.78	48.77		0.07	0.931
	4	358	50.71	49.99	50.51	50.89			0.14	0.937	145	52.61	49.86	47.47	50.31	0.96	0.415
		5,667					0.93	0.394	0.13	0.940	1,675					0.36	0.780
Openness to experience	2	3,984	50.74	49.94					6.71	0.010	1,020	49.94	49.87			0.02	0.893
	3	1,325	50.80	49.96	50.35				0.63	0.534	510	51.34	49.57	49.23		2.24	0.108
	4	358	49.48	50.23	50.18	48.07			0.70	0.550	145	49.37	51.01	49.36	52.90	0.58	0.628
		5,667					0.37	0.692	2.96	0.031	1,675					0.87	0.454
Imagination	2	3,020	50.49	49.98					1.95	0.163	452	49.41	48.94			0.30	0.585
	3	1,021	50.62	49.80	50.35				0.62	0.536	151	50.06	50.16	49.87		0.03	0.970
	4	285	49.49	50.21	49.69	49.14			0.12	0.946	29	48.32	48.72	45.19	50.87	0.40	0.755
		4,326					0.25	0.778	0.94	0.423	632					0.31	0.815
Intellect	2	3,020	51.16	49.57					20.45	<0.001	452	51.38	49.56			4.88	0.028
	3	1,021	50.49	49.64	50.09				0.63	0.533	151	51.07	47.56	47.30		2.42	0.096
	4	285	51.02	50.30	50.84	49.01			0.58	0.631	29	51.12	51.56	47.14	49.80	0.37	0.776
		4,326					0.60	0.549	7.30	<0.001	632					3.27	0.022
Intelligence (IQ)	2	1,921	102.94	100.77					11.66	<0.001	688	101.83	98.78			19.62	<0.001
	3	623	101.92	97.65	101.08				4.65	<0.001	410	102.43	100.49	98.74		1.88	0.155
	4	156	99.07	100.00	97.51	96.96			0.29	0.830	123	100.72	101.39	96.52	97.80	1.07	0.367
		2,700					4.68	<0.001	6.01	<0.001	1,221					7.36	<0.001

The NCDS sample could not be included in this analysis because it was missing information on the age gaps between siblings.