Individual data could provide more insight into potential confounding associations.
As in the general case of bias discussed above, confounding would more easily generate a weak (spurious) association than a strong one.
Third, several third factors can confound associations in observational studies.
There are difficulties in conducting epidemiologic studies of agents that are relatively "weak" carcinogens, or for stronger carcinogens where exposure is very low because bias and confounding can obscure weak positive associations (MacMahon et al. 1981).
This was an observational analysis and therefore not able to provide information on causal relationships and, due to the moderate effect sizes observed, it is possible for unmeasured confounding to explain the weak observed associations.
Additional adjustment for BMI to explore residual confounding showed weaker nonsignificant associations, but it is questionable whether inclusion of BMI represents overadjustment because BMI and sex hormone levels are on the same pathway.
(The weak association found in the univariate analysis was probably confounded by contact with the patient's body fluids).
All the underlying studies suffer from the usual fatal flaws of weak association epidemiology: here that means, no knowledge of actual meat consumption, confounding risk factors for pancreatic cancer or biological plausibility' (Milloy, 2012).
The results from the few previous epidemiological studies finding weak positive associations between smoking and CRC have been explained as confounded by alcohol and other dietary risk factors [ 6, 21].
There was a weak association between blood lipid profile and physical fitness in both urban and rural adolescents, even after adjustment for confounding factors.
Epidemiology, therefore, faces the challenge of identifying the weak causal associations that require large study populations and taking special care to exclude bias and confounding, and it is not surprising that the evidence on which these associations are based is often challenged.
