Comment on 'Childhood leukaemia close to high-voltage power lines--the Geocap study, 2002-2007'--odds ratio and confidence interval.

Sir,

The precision of the odds ratio (OR) test is estimated by the 95% confidence interval, which is interpreted as significant when its values do not overlap the 1.0 null value (Szumilas, 2010). In this context, some sentences of the results section in the paper by Sermage-Faure are unwarranted. These sentences are ‘an association was evidenced for children who lived within 50 m of a VHV-HVOL (OR=1.7 (0.9–3.6))' ‘The results for ALL were very similar (OR=1.9 (0.9–4.0) at <50 m from a VHV-HVOL)' ‘In that age group, living within 50 m of the closest VHV-HVOL was significantly associated with AL (OR=2.6 (1.0–7.0))' and ‘Sensitivity analyses restricted to the best geocoded subjects (uncertainty ⩽20 m) generated slightly stronger results (OR=2.1 (0.9–4.7) for living within 50 m of a VHV-HVOL)'. Inasmuch as all these confidence intervals intersect the 1.0 null value, they must not be interpreted as significant ones. Therefore, the conclusion that ‘living <50 m from a 225 or 400 kV HVOL may be associated with an increased incidence of childhood AL' is biased by this statistical concern. This situation contains a strong potential to generate confusion, distorts the knowledge, and hampers the understanding of the acute leukaemia aetiology.