Eligibility criteria
Eligible articles included systematic reviews and meta-analyses of
observational epidemiological studies that examined the association of
potential risk factors with childhood cancer types. Exposure variables
included environmental exposures of either parent (mother and/or father)
or child during preconception, pregnancy, delivery or childhood. Outcome
variables included any type of cancer diagnosed in children aged 0-14
years. Studies on broader age groups which included sub-analyses on
children 0-14 years were also eligible. Meta-analyses that solely
examined the association of genetic or epigenetic factors with childhood
cancer risk were excluded. Likewise, meta-analyses that investigated
cancer survival or other outcomes among patients with cancer, as well as
meta-analyses not reporting comprehensive study-specific information,
such as effect sizes, 95% confidence intervals (CI) or sample sizes
were also excluded. When one or more eligible systematic reviews and/or
meta-analyses on the same research question were identified, the one
with the largest number of component studies, usually the most recently
published study, was included. Each identified study was cross-checked
for each quality and issues of overlap before including in the final set
of eligible studies.