We did correct for level of education, fatherhood, retirement and cohabitation, although it can be problematic to control for social factors, because the chromosome aberrations per se can be the very reason for social problems, while the reverse is not possible.
Recreational outbreaks associated with sprayparks are well recognized, and may be partly due to the engineering designs used for their water reclamation systems are problematic to control.
Epidemiology is the study of the link between exposure, outcome and confounders, but the measurement of exposure to outdoor pathogens in the air is difficult, as it is problematic to conduct controlled laboratory experiments, for example, to expose people to pathogens within the laboratory.
It is problematic to use a control group in a study such as this simply because several of the control group members received other kinds of treatment during the follow-up period.
As CycD and Rb are two genes deciding network states to be either desirable or undesirable, it is problematic to apply the MFPT control policy if these genes are considered.
25 Negative fatalistic perspectives are problematic to cancer control because those holding more fatalistic views are less likely to participate in cancer screening or engage in cancer protective behaviours such as exercise, not smoking and eating more than five fruits and vegetables each day.
This type of contamination, occurring before sampling, is most problematic as it is impossible to control for [26].
Open ponds are problematic, says Briggs, because it's hard to control species distribution.
The pursuit of uncommon variants using case-control designs is problematic due to the need for genotyping even larger numbers of controls, due to their rarity in the population.
Direct comparison of these populations is problematic because pest control strategies may have changed over the 4 years that separated these studies.
