Since a-ZAL was the only chemical d

Since a-ZAL was the only chemical detected in a large enough
sample size, statistical analyses were performed only for a-ZAL
in order to determine the association between the exposure to this
chemical and the presence of breast cancer. Descriptive statistics
are reported as mean, median and range. Crude and adjusted odds
ratios (ORs) with 95% confidence intervals (CIs) were calculated by
unconditional logistic regression to estimate the magnitude of the
association between a-ZAL and breast cancer. The concentration of
this compound was used as independent variable and analyzed as
continuous variable. a-ZAL concentrations below the LOD were
assigned a value of LOD divided by the square root of 2.
In the bivariate analysis, differences between groups were
tested with Pearson’s chi-square test or Fisher’s exact test, when
appropriate. Potential confounding variables were selected if they
were significantly associated with a-ZAL concentrations and with
the risk of cancer. In the final adjusted model, only age, number
of children, social class, type of water consumed and vegetable
consumption were considered confounding variables. All statistical
analyses were performed using SPSS statistical software for Windows
version 20.0 (SPSS Inc., Chicago, IL, USA) and the R statistical
computing environment v3.0