How identity fusion predicts extreme pro-group orientations: A meta-analysis

Figures & data

Figure 1. PRISMA flow-chart.

Table 1. Results of robust variance estimation meta-analyses.

Model/Variable	k effects	k studies	Estimate	95% CI-L	95% CI-U	p	dfs	I^2	τ^2
Model 1: Main effect	106	90					89	90.60	.03
Intercept (Identity fusion)			.495	.461	.528	< .001
Model 2: Demographics	101	85					82	90.11	.03
Intercept			.508	.424	.583	< .001
Men (%)			−.001	−.003	.002	.601
Age			−.071	−.117	−.024	.004
Model 3a: Construct type(all studies)	138	90					88	90.80	.03
Intercept (Social identification)			.368	.294	.438	< .001
Identity fusion			.160	.077	.238	< .001
Model 3b: Construct type (matched studies)	64	30					28	89.74	.03
Intercept (Social identification)			.368	.290	.441	< .001
Identity fusion			.138	.086	.190	< .001
Model 4: Country	106	90					81	89.45	.03
Intercept (Spain)			.481	.438	.521	< .001
Brazil			−.079	−.177	.021	.119
China			−.027	−.081	.027	.325
Italy			.391	.342	.438	< .001
Norway			−.014	−.068	.040	.605
Poland			.126	−.096	.335	.262
U.K.			−.335	−.382	−.286	< .001
U.S.			.070	−.057	.195	.276
Worldwide			−.031	−.086	.025	.271
Model 5: Target group	105	89					83	90. 63	0.03
Intercept (National group)			.480	.442	.516	< .001
Kinship			−.065	−.112	−.017	.008
Other groups			.033	−.139	.204	.705
Outgroup			.214	.052	.364	.010
Political group			−.122	−.254	.013	.076
Religious group			.195	−.291	.601	.431
Model 6: Fusion measure type	105	89					86	90.40	0.03
Intercept (Identity fusion, verbal)			.519	.482	.554	< .001
Dynamic Identity Fusion Index (DIFI)			−.228	−.376	−.068	.006
Pictorial scale			−.142	−.249	−.032	.012
Model 7: DV measure type	101	88					85	90.33	0.03
Intercept (Fight/Die/Sacrifice)			.486	.448	.522	< .001
Extreme Collective action			.184	.042	.318	.012
Outgroup hostility			−.068	−.120	−.016	.011

Note. Model 1 refers to the main effect of identity fusion on outcomes, whereas Model 2–7 refer to meta-regression models with moderators. Names in parentheses next to the intercept indicate what category was used as baseline in the specific meta-regression. Estimate refers to regression coefficients (back-transformed to r). ^aAge was standardised. ^bThese analyses were conducted only on studies that measured both identity fusion and social identification. Statistically significant estimates are presented in bold.

Figure 2. Estimated effect size for models 2 through 7.

Note: Error bars or ribbons represent 95% CIs. Black points represent observed mean effects, whereas grey points represent effects for each study.

Table 2. Results of robust variance estimation meta-analyses comparing identity fusion scales against social identity measures.

	k
Reference/Comparison Variables	studies	effects	Estimate	95% CI-L	95% CI-U	p	dfs	I^2	τ^2
Verbal Identity Fusion Scale	71	85					81	91.25	.03
Intercept	-	-	.525	.477	.570	<.001
Mael and Ashforth (1992)	33	60	−.084	−.185	.019	.107
Ellemers et al. (1999)	2	4	−.255	−.322	−.184	< .001
Leach (2008)	3	6	−.204	−.283	−.123	< .001
Postmes et al. (2013)	1	1	−.021	−.085	.044	.524
Steffens et al. (2015)	1	2	−.158	−.220	−.095	< .001
Pictorial Identity Fusion Scale	14	14					81	91.25	.03
Intercept	-	-	.247	.158	.333	<.001
Mael and Ashforth (1992)	33	60	.242	.123	.354	< .001
Ellemers et al. (1999)	2	4	.070	−.030	.168	.165
Leach (2008)	3	6	.123	.016	.227	.024
Postmes et al. (2013)	1	1	.301	.214	.383	< .001
Steffens et al. (2015)	1	2	.170	.078	.258	< .001
Dynamic Scale	4	6					81	91.25	.03
Intercept	-	-	.338	.186	.473	<.001
Mael and Ashforth (1992)	33	60	.147	−.034	.318	.110
Ellemers et al. (1999)	2	4	−.029	−.193	.137	.734
Leach (2008)	3	6	.025	−.146	.194	.776
Postmes et al. (2013)	1	1	.208	.048	.358	.012
Steffens et al. (2015)	1	2	.072	−.091	.231	.381

Note. Please not that all models also included the respective alternative identity fusion scales. These are not included to keep presentation parsimonious. Significant comparisons are presented in bold.

Table

Author	Year	Country	N	Male (%)	Mean age	Fusion scale	Outcome scale	Fusion type
Besta et al.	2014	Poland	109	44	27.76	Verbal	Fight and die	Religion
	2014	Poland	365	46	21.84	Verbal	Fight and die	Country
Besta	2014	Poland	203	69	34.2	Pictorial	Fight and die	Country
Besta et al.	2015	Poland	155	52.26	19.6	Verbal	Fight and die	Country
		Poland	24	91.67	22.9	Verbal	Fight and die	Country
Besta & Kossakowski	2018	Poland	568	88.56	27.02	Verbal	Collective action	Other groups
Bortolini et al.	2018	Brazil	387	45.2	28.9	Verbal	Fight and die	Country
		Brazil	372	33.3	30.4	Verbal	Fight and die	Religion
		Brazil	401	47.6	30.4	Verbal	Fight and die	Other groups
Buhrmester et al.	2015	U.S.	80	38	26	Verbal	Support actions	Country
		U.S.	120	46	37.3	Verbal	Fight/die/sacrifice	Country
		U.S.	133	42	34	Verbal	Donations, Support actions	Country
Carnes & Lickel	2018	U.S.	204	41.7	35.44	Verbal	Fight and die	Country
Chinchilla et al.	Unpublished	Spain	338	43.2	35.59	Verbal	Fight/die/sacrifice	Country
Chinchilla et al.	Unpublished	Spain	321	64.5	38.72	Verbal	Fight/die/sacrifice, Costly sacrifice	Country
Chinchilla et al.	Unpublished	Italy	114	66.7	33.42	Verbal	Collective action, Fight and die	Outgroup
Chinchilla et al.	Unpublished	Italy	78	27.2	27.85	Verbal	Collective action	Outgroup
Chinchilla et al.	Unpublished	Spain	197	36.5	36.97	Verbal	Collective action	Outgroup
Chinchilla et al.	Unpublished	Spain	424	46.7	35.52	Verbal	Fight/die/sacrifice, Outgroup hostility	Country
Chinchilla et al.	Unpublished	Spain	424	36	31.76	Verbal	Fight/die/sacrifice, Outgroup hostility	Country
Gómez et al.	2011a	Spain	86	36.05	33.42	Pictorial	Fight and die	Country
		Spain	460	19.13	32.1	Pictorial	Fight and die	Country
		Spain	194	21.13	34.22	Pictorial	Fight and die	Country
Gómez et al.	2011b	Spain	620	27	32.64	Verbal	Fight and die	Country
		Spain	92	42.4	33.88	Verbal	Fight/die/sacrifice	Country
		Spain	93	49.5	34.09	Verbal	Fight/die/sacrifice	Country
		Spain	79	15.2	31.05	Verbal	Fight and die	Country
		Spain	37	13.5	30.86	Verbal	Fight and die	Country
		U.S.	357	33	34.79	Verbal	Fight and die	Country
		Spain	1981	28	31.64	Verbal	Fight and die	Country
Gómez et al.	2019	Spain	1151	37	37.11	Verbal	Fight and die	Country
		Spain	458	41	37.14	Verbal	Fight and die	Country
Heger & Gaertner	2018	U.S.	190	46	NA	Verbal	Fight and die	Other groups
		U.S.	189	43	NA	Verbal	Fight and die	Other groups
Jiménez et al.	2016	Spain	95	20	34.78	Dynamic	Fight and die	Country
Kavanagh et al.	2019	World	605	95.4	31.27	Verbal	Outgroup prejudice	Other groups
Kossakowski & Besta	2018	Poland	309	87.4	26,00	Verbal	Extreme endorsement	Other groups
Kunst et al.	2018	Norway	215	40.9	24.99	Verbal	Extreme protest	Outgroup
		U.S.	201	56.7	34.6	Verbal	Extreme protest	Outgroup
		U.S.	234	45.7	36.13	Verbal	Extreme protest	Outgroup
		U.S.	83	96.3	31.6	Verbal	Fight/die/sacrifice	Outgroup, Country
Kunst et al.	2019	U.S.	176	41.5	43.19	Verbal	Political extremism, Policy support	Political
		U.S.	171	49.8	43.18	Verbal	Political extremism	Political
		U.S.	176	46.6	45.09	Verbal	Terror support	Political
Lopez Rodriguez et al.	Unpublished	Spain	204	43.6	38.86	Dynamic	Extremity of sacrifice, Fight/die/sacrifice, Spanish costly sacrifice	Country
Lopez Rodriguez et al.	Unpublished	Spain	193	32.6	36.92	Dynamic	Fight/die/sacrifice	Country
Lopez Rodriguez et al.	Unpublished	Spain	176	40.9	35.62	Dynamic	Fight/die/sacrifice	Country
Lopez Rodriguez et al.	Unpublished	Spain	248	48.8	36.89	Dynamic	Fight/die/sacrifice	Country
Newson et al.	2018	Brazil	465	95	25.72	Verbal	Fight and die	Other groups
Martinez et al.	Unpublished	Spain	199	40.2	39.92	Pictorial	Fight/die/sacrifice	Country
Martinez et al.	Unpublished	Spain	613	38.1	37.09	Verbal	Fight/die/sacrifice	Country
Martinez et al.	Unpublished	Spain	525	34.1	35.97	Verbal	Fight/die/sacrifice	Country
Paredes et al.	2018	Spain	155	25	35.21	Verbal	Fight and die	Country
Paredes et al.	2019	Spain	299	38	35.88	Verbal	Fight and die	Country
		Spain	607	35	34.51	Verbal	Fight and die	Country
		Spain	483	44	37.19	Verbal	Fight/die/sacrifice	Country
Paredes et al.	Unpublished	U.S.	113	-----	-----	Verbal	Fight/die/sacrifice	Country
Paredes et al.	Unpublished	U.S.	113	-----	-----	Verbal	Fight/die/sacrifice	Country
Paredes et al.	Unpublished	Spain	113	-----	-----	Verbal	Fight/die/sacrifice	Country
Paredes et al.	Unpublished	Spain	113	50.6	27.65	Verbal	Fight/die/sacrifice	Country
Swann et al.	2014a	World	2438	35	24.06	Verbal	Fight and die	Country
		China	82	48.2	20.82	Verbal	Fight and die	Country
Swann et al.	2014b	Spain	85	20	31.4	Verbal	Self-sacrifice	Country
		Spain	293	46.1	36.71	Verbal	Self-sacrifice	Country
		Spain	436	44.5	33.9	Verbal	Self-sacrifice	Country
		Spain	572	34.1	33.21	Verbal	Self-sacrifice	Country
		Spain	1368	44.17	35.14	Verbal	Self-sacrifice	Country
		Spain	622	42.6	34.48	Verbal	Self-sacrifice	Country
Swann et al.	2010	Spain	62	53.23	33.47	Pictorial	Fight/die/sacrifice	Country
		Spain	207	20.3	34.23	Pictorial	Fight/die/sacrifice	Country
		Spain	66	27.27	37.24	Pictorial	Fight/die/sacrifice	Country
		Spain	171	28.65	36.07	Pictorial	Fight/die/sacrifice	Country
Swann et al.	2009	Spain	177	42.94	33.05	Pictorial	Fight and die	Country
		Spain	602	13.62	31.17	Pictorial	Fight and die	Country
		Spain	326	14.72	31.06	Pictorial	Fight and die	Country
		Spain	429	11.95	15.81	Pictorial	Fight and die	Country
Talaifar & Swann	2019	U.S.	303	44.6	36.6	Verbal	Fight and die	Country
Vázquez et al.	2015	Spain	1522	41.6	32.28	Verbal	Fight and die	Country
Vázquez et al.	2019	Spain	248	41	31.95	Verbal	Fight and die	Kinship
Vasquez et al.	Unpublished	Spain	193	51.8	15.32	Verbal	Fight/die/sacrifice	Country
Vasquez et al.	Unpublished	Spain	111	54.9	15.52	Verbal	Fight/die/sacrifice	Country
Vasquez et al.	Unpublished	Spain	122	49.1	15.7	Verbal	Fight/die/sacrifice	Country
Vasquez et al.	Unpublished	Spain	109	34.8	34.92	Verbal	Fight/die/sacrifice	Country
Vasquez et al.	Unpublished	Spain	1245	40.2	35.27	Verbal	Fight/die/sacrifice	Country
Vasquez et al.	Unpublished	Spain	792	35.4	33.48	Verbal	Fight/die/sacrifice	Country
Vasquez et al.	Unpublished	Spain	355	41.4	36.78	Verbal	Fight/die/sacrifice	Country
Vasquez et al.	Unpublished	Spain	250	44.8	32.31	Verbal	Fight/die/sacrifice	Country
Vasquez et al.	Unpublished	Spain	308	46.8	33.24	Verbal	Fight/die/sacrifice	Country
Vasquez et al.	Unpublished	Spain	806	38.8	36.24	Verbal	Fight/die/sacrifice	Country
Whitehouse et al.	2017	U.S.	122	46.2	37.74	Verbal	Extreme endorsement	Country
		U.K.	725	88.9	39.5	Verbal	Fight and die	Other groups

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Data availability statement

The full dataset, R code, and supplementary online materials (SOM) are available via https://osf.io/za4rj/?view_only=3980c9e81fac401e83ce6837f41e4f67.