However, we did not observe an upward trend with increasing level of cumulative exposure (P=0.096), nor by frequency, intensity or duration of exposure, although the Fisher test for combined probabilities was of borderline significance (P=0.050).
The reciprocal independence between the categorical metrics of frequency, intensity and duration of exposure was previously assessed ( 25 ), which provided the conditions to apply the Fisher method for combined probability testing to calculate the chance probability associated with a positive trend observed with these three independent tests bearing upon the same overall hypothesis ( 26 ).