CCRG “wrap up” paper

The Childhood Cancer Research Group (CCRG), working in conjunction with National Grid, have published a series of epidemiological studies of childhood cancer and power lines, underground cables, and related factors in the UK, starting in 2005 - see the complete list.  The most recent, and the final planned paper, was published in June 2016.  It comprises a number of subanalyses or follow-up analyses to do with overhead lines that didn't make it into the previous papers.  We summarise the key findings below.

The CCRG's 2014 paper found that the elevated risks close to power lines were highest in the 1960s and declined in the subsequent decades.  Most of the analyses in this new paper are therefore primarily concerned with the risk in the earlier years.  The graphs illustrate the relative risk in the 0-200 m band compared to >1000 m from the power lines.

Age of child at diagnosis

There seems to be a slight trend for the risk (when it was present at all, in the earlier years as shown by the red line in the graph below) to be greater for older children:

graph of ccrg risks by age of child


Subtypes of leukaemia

There is a suggestion that the risk is higher for myeloid leukaemia (the blue line on the following graph - the majority of leukaemias are lymphoid, the green line):

graph of ccrg risks for leukaemia subtypes


Region of the country

There is no very obvious pattern for whether the risk is higher in any particular regions of the country, although perhaps just a suggestion of higher risks in more urban regions:

graph of ccrg risks by region of country

This shows the risks for the period 1962-1989 only.  Risks in the last three regions were indeterminate.

Calendar year or age of line?

The CCRG found risks that were highest in the 1960s and declined over the decades since.  But this graph shows when the power lines in the UK were built:graph showing ages of power lines

So in the 1960s, the power lines tended to be newer, and the decline in risk that the CCRG found could be described or explained in two different ways:

  • A calendar-year effect: some aetiological factor was present in the 1960s, has declined over time, and is no longer present in the 2000s.
  • A time-from-construction effect: the construction of a power line produces a transient effect in its vicinity that lasts a decade or so, producing the declining risk over time.

The paper performs a lot of analysis to try to distinguish these two possibilities, though as the two factors - calendar year and age of line - are highly correlated, it was never going to be possible to separate them conclusively.  The conclusion is that it seems the effect probably really is calendar year.  This is suggested (weakly) by the following graph (the risks analysed by calendar year, the red line, are bigger than when analysed by age of line, the blue line), and a multivariate analysis presented in the paper seems to show the same thing rather more clearly.

graph comparing ccrg risks by year and by age of line

The paper spells out the public-health implications of this distinction:

If the effect is linked to calendar year, either of birth or of cancer occurrence, then it is now no longer present, and any new power lines constructed today would not be expected to produce this effect. If, however, it is a transient effect linked to the construction of a power line, any new power lines constructed today could still be expected to produce this effect.

The paper then concludes:

We therefore conclude that it seems more likely that our risks are explained by a factor present in the 1960s and declining thereafter, rather than by a factor present when a new line is constructed and declining thereafter. We therefore also conclude, with similar cautiousness, that we would not expect any new power line constructed today to produce equivalent risks. However, with the two variables so highly correlated and producing similar risks when analysed separately, this analysis cannot be definitive.

Magnetic-field update

The final analysis in the paper is to update the calculated magnetic fields for the newer subjects in the study.  The numbers involved are too small to be particularly important in their own right, but the paper explains that the main use will be to include them in any future pooled analysis, just as the first set of calculated magnetic fields from this study were included in the Kheifets et al pooled analysis.

The abstract of the paper

J. Radiol. Prot. 36 (2016) 437–455
Epidemiological study of power lines and childhood cancer in the UK: further analyses
K J Bunch, J Swanson, T J Vincent and M F G MurphyWe report further analyses from an epidemiological study of childhood cancer and residence at birth near high-voltage power lines in the UK. These results suggest that the elevated risks for childhood leukaemia that we previously found for overhead power lines may be higher for older age at diagnosis and for myeloid rather than lymphoid leukaemia. There are differences across regions of birth but not forming any obvious pattern. Our results suggest the decline in risk we previously reported from the 1960s to the 2000s is linked to calendar year of birth or of cancer occurrence rather than the age of the power lines concerned. Finally, we update our previous analysis of magnetic fields to include later subjects.

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