Many communities add fluoride to their drinking water to prevent tooth decay. However, fluoride crosses the placenta and laboratory studies show that it accumulates in brain regions involved in learning and memory. A study of 512 Canadian women found that fluoride exposure during pregnancy was associated with lower IQ scores in children. The article states that “A 1-mg higher daily intake of fluoride among pregnant women was associated with a 3.66 lower IQ score in their children.”

(a) Is this an experiment or an observational study?

(b) What is the explanatory variable? What is the response variable?

(c) Is the correlation between these two variables positive or negative?

(d) What specific quantity is being described in the quoted sentence?