Study Background for Data Analysis Section

Study Background for Data Analysis Section 

The NC State Health Director charged your team to investigate the health effects of a GenX chemical spill from the Chemours chemical plant into the lower Cape Fear river basin.  GenX (perfluoro-2-propoxypropanoic acid) is part of a large chemical class of per- and polyfluoroalkyl substances (PFAS) and is used to make Teflon.  While PFOA and PFAS have been studied, less is known about GenX health effects. You completed your analysis on the cohort study, in which you examined the potential relationship between GenX exposures in drinking water and elevated liver enzymes. On going water monitoring indicates exposures above the 140 ng/L cutpoint as recently as last year. 

Your initial findings of an association between GenX exposure and increased risk of elevated liver enzymes (Exam 1) generated substantial interest from the NC State Health Director, their staff, and people living in Wilmington and along the Cape Fear River. 

You’ve now been asked to conduct a case control study of liver cancer and GenX exposure. You and your team were awarded a NC Division of Public Health contract to review the literature, conduct analyze a case control study, and interpret your results.  You used the North Carolina Central Cancer Registry to locate 51 people with newly diagnosed liver cancer. You randomly selected and recruited 51 people from the North Carolina Department of Motor Vehicles registry to serve as controls.  Your colleagues have asked you to consider potential sources of systematic error.  Note this example is instructional, however, increased PFOS exposures have recently been reported to associated with increased odds of liver cancer, see Cao L, Guo Y, Chen Y, Hong J, Wu J, Hangbiao J. Per-/polyfluoroalkyl substance concentrations in human serum and their associations with liver cancer. Chemosphere. 2022 Jun;296:134083.

Consider the measurement of the exposure, GenX, in the case control study. Initially researchers asked study participants with liver cancer (cases), and a comparison group of study participants without liver cancer (controls) about GenX exposures (including water consumption amounts and sources) over the past ten years.  

a) Identify the specific type of systematic error that could arise, with specific mention of misclassification. (Hint: Do you think there could be differential or nondifferential misclassification of the outcome, based on exposure status?  Or do you think there could be differential or nondifferential misclassification of the exposure, based on the outcome status? Provide a rationale.) 

b)Describe an alternative approach to collecting exposure information that would minimize this systematic error.