Table 2.

Association of dioxin exposure (modelled ground-level concentrations) with non-Hodgkin's lymphoma incidence (3974 cases, four administrative departments, 1990–1999, France)

	Regression coefficient	Standard deviation	P-value
	Univariate analysis
Dioxin exposure*	1.453	0.328	10-5
	Multivariate analysis
Dioxin exposure	0.925	0.459	0.04
Department
Isère†	-	-	-
Bas-Rhin	0.094	0.042	0.03
Haut Rhin	0.008	0.046	0.87
Tarn	-0.180	0.058	0.002
Log(industry × years)	0.022	0.011	0.05
S(log(population density))‡	-	-	0.07

* modelled ground-level concentrations

^† reference category

^‡ spline-smoothed log(population density) with 1.963 effective degrees of freedom.

Neither a regression coefficient nor a standard deviation can be reported, as for any spline curve (divided by definition into many segments corresponding to the knots).