Evaluation of Mobile Phone and Cordless Phone Use and Glioma Risk Using the Bradford Hill Viewpoints from 1965 on Association or Causation

Table 10

Biological Gradient. Numbers of cases (Ca), controls (Co), and odds ratio (OR) with 95% confidence interval (CI) for cumulative duration of calls (hours) in Coureau et al. [39].

Cumulative duration of calls (hours)	Ca/Co	OR (95% CI)
No use	107/211	(1.0)
<43	24/63	0.83 (0.48–1.44)
43–112	20/55	0.77 (0.42–1.41)
113–338	28/58	1.07 (0.60–1.90)
339–895	28/37	1.78 (0.98–3.24)
≥896	24/22	2.89 (1.41–5.93)
value global test		0.02