Table 7.

Robustness checks

	OR	ME
Base case model
GPs per 1000 patients	2.453**	0.203***
Distance to practice (km)	0.918**	−0.020**
Quadratic functional form
GPs per 1000 patients	5.957
GPs per 1000 patients squared	0.535
Distance to practice (km)	0.779*
Distance to practice (km) squared	1.030
Cubic functional form
GPs per 1000 patients	0.400
GPs per 1000 patients squared	33.953
GPs per 1000 patients cubic	0.130
Distance to practice (km)	0.918
Distance to practice (km) squared	0.963
Distance to practice (km) cubic	1.007
Adding IMD 2004 variables
GPs per 1000 patients	2.982***
Distance to practice (km)	0.925**
Adding secondary care indicators
GPs per 1000 patients	2.699***
Distance to practice (km)	0.953
Using IMD 2004 variables as instruments
GPs per 1000 patients	N/A	0.373***
Distance to practice (km)	N/A	−0.024
Adding IMD 2004 and secondary care indicators
GPs per 1000 patients	3.155***
Distance to practice (km)	0.946

OR odds ratio, ME marginal effect, GP general practitioner

* P < 0.1, ** P < 0.05, *** P < 0.01. Controls are included in every model for demographics, marital status, ethnic group, self-reported health, education, employment status, household financial wealth, demographic profile of the area and percentage with no qualifications in area of residence