A researcher studying fluoride absorption wants to control for a confounding variable. Which factor could most affect the ACCURACY of the study?

Correct answer: B. Difference in fluoride concentration across natural water sources

• A. Sex differences in fluoride absorption are a potential confound but can be controlled through study design.
• B. Variation in fluoride CONCENTRATION across different natural water sources is a critical confounding variable that could directly affect fluoride absorption measurements. If subjects are consuming water with different fluoride concentrations, the study cannot accurately measure the effect of fluoride on the outcome — this would be a major source of bias and inaccuracy.
• C. Test/measurement failures are a reliability issue, not a confounding variable specifically related to fluoride absorption accuracy.
• D. Altitude might affect some physiologic parameters but is not the primary confound for a fluoride absorption study.