Table 3.

Scaled coefficients for covariates of the Pomp models, and information criterions for these models

	GDP per capita	Diff	GDP per capita × Diff	Cum	GDP per capita × Cum	Cum_diff	AIC	BIC
A							304.8	321.4
B							148.9	168.3
C	0.07						136.9	159.1
D				0.09			150	172.1
E	0.074				0.004		138.9	163.8
F		0.025					148.7	170.9
G	0.065	0.009					138.6	163.5
H			0.042				148.4	170.6
I	0.068		0.013				138.5	163.4
J						0.029	145.9	165.3
K	0.086	−0.087	−0.067	−0.237	−0.1	0.184	138.8	172

‘Diff’ stands for horizontal diffusion (the sum of productions of neighbouring countries divided by the squares distance between capital cities). ‘Cum’ stands for the cumulative estimated scientific production of a country before that time – i.e. vertical diffusion. ‘Cum_diff’ stands for the cumulative horizontal diffusion. The models A and B are excluded, as they use no covariate. The coefficients of model K are difficult to interpret, some covariates like horizontal diffusion having a negative effect. This is due to high covariance between covariates, especially when interactions are included.