Why do only some people who support parties actually join them? Evidence from Britain

Figures & data

Table 1. Social and political characteristics of British political party members and supporters, 2015.

Attribute	Supporters	Members	N	Significance
Mean age	52	51	12,069	*
% male	48.0	65.0	12,072	***
% graduates	32.1	46.2	11,780	***
% ABC1	59.1	77.6	11,914	***
Mean left–right
Left parties	1.99	1.75	7,660	***
Conservative Party	5.08	6.34	2,264	***
UKIP	2.62	3.59	1,790	***
Mean left–right extremism
Left parties	–0.09	0.08	7,660	***
Conservative Party	–0.62	0.64	2,264	***
UKIP	–0.41	0.56	1,790	***
Mean liberty–authority
Left parties	5.40	3.93	7,317	***
Conservative Party	7.39	6.58	2,232	***
UKIP	7.97	7.54	1,790	***
All parties	6.22	4.99	11,339	***
Personal efficacy	4.18	6.28	11,758	***
Group efficacy	5.13	7.33	10,855	***
Expressive incentives	6.34	8.28	12,053	***
Altruism	5.80	7.07	11,649	***
Selective process	5.76	7.15	11,076	***
Selective outcome	5.11	6.54	11,130	***
% Social norms	29.6	48.2	12,071	***
Cost of activism	6.87	6.44	11,001	***

Source: PMP; * p < 0.05; ** p < 0.01; *** p < 0.001.

Table 2. Logistic regression of party membership, 2015.

	M1		M2
	(N = 8714)		(N = 8714)
	B	SE	B	SE
Male	0.63	0.05***	0.81	0.06***
Graduate	0.18	0.06***	0.30	0.07***
Age	0.03	0.02*	0.04	0.02*
Social grade	0.52	0.06***	0.63	0.07***
Socially liberal/authoritarian (0–10)	−0.18	0.01***	−0.20	0.02***
Left–right extremism (−8.5/7)	0.16	0.02***	0.06	0.02***
Personal efficacy (0–10)	0.54	0.01***	0.26	0.02***
Group efficacy (0–10)			0.48	0.02***
Expressive incentive (Very strong vs. Fairly strong party id)			1.45	0.06***
Altruism (0–10)			0.10	0.01***
Selective outcome (0–10)			0.05	0.01***
Selective process (0–10)			0.13	0.02***
Social norms (member of other organisations vs. non-member)			0.83	0.06***
Cost of activism			−0.10	0.02***
Constant	−2.26	0.18***	−8.97	0.32***
Pseudo-R2	25.6		44.5

Source: PMP; * p < 0.05; ** p < 0.01; *** p < 0.001.

Note: A control for parties has been included in the two models but is not shown here in order to simplify presentation.

Table 3. Comparing perceptions of membership incentives though direct and analogous questions.

	Supporters	Members	Significance
Expressive incentives
Attachment to party’s principles	8.24	9.21	***
Belief in party’s leadership	7.73	7.89	***
Collective incentives
Support policies	8.30	9.20	***
Oppose policies	7.82	7.72	***
Altruism
Support democratic process	7.17	8.56	***
Promote national interest	6.88	8.88	***
Selective process	7.55	5.59	***
Selective outcome	6.49	2.06	***
Social norms	5.71	2.98	***

Source: PMP; * p < 0.05; ** p < 0.01; *** p < 0.001. N = 12,069.

Note: Highlighted incentives are those which supporters score more highly than members.