Average annual concentrations of nitrate during the years studied are not statistically different, but interaction between proximity and years is statistically significant (F = 2.07; p = 0.04).
The differences between the two years are statistically significant (X2 = 12.5; 3 df, 0.001 < P < 0.01), mainly due to a shift in 2009 2010 toward the "insufficient knowledge" response.
In 1994 and 1998 the mean avidity values were 49 (SD ± 16.0) and 71 (SD ± 14.2), respectively, and the difference between the 2 years was statistically significant (p < 0.001).
The differences between the two level 1 years are statistically significant (X2 = 19.1; 3 df; P < 0.001) but the overall pattern of responses was the same.
Average values of nitrate during the years are not statistically different, but the interaction between point source distance (proximity) and years is statistically significant (F = 2.07; p = 0.04), which indicates that the concentration of nitrate during the monitoring does not behave the same with respect to the distance (Fig. 3).
The difference in mean ages between cases (66 years) and controls (62 years) was statistically significant (p = 0.001).
Although the intra-cluster correlations for associations between variables across each year were statistically significantly different for some outcomes, in these instances the ICCs were very small and the difference between samples was less than 0.01.
The differences in incidence rates amongst counties between each subsequent and preceding year were statistically tested and only the increase from 2008 to 2009 was statistically significant (p < 0.05) (Table 3).
Generalized Estimating Equations (GEE) analyses showed that differences between the groups considered over one year were statistically significant regarding an improvement in pain (p = 0.002), and disability on CPQ (p = 0.005) and disability on WDQ (p < 0.001), favoring the Index Group.
The findings of the present study were that the clinically and statistically significant differences in pain intensity and disability between the groups remained at 26 and 52 weeks, and that the differences between the groups considered over one year were statistically significant (p < 0.01) also when consideration was taken to the covariance between the repeated measurements.
