Biology of Humans 6th Edition by Judith Goodenough,Betty McGuire

Exercise 11

Beginning at puberty and throughout his life, a male produces millions of sperm a day. During sperm development and maturation, a process that requires months, sperm are vulnerable to certain environmental influences, including environmental pesticides. Researchers1 from the Harvard T. H. Chan School of Public Health have reported that pesticide residues of food can affect sperm development. The excerpt below is from "Eating fruits and vegetables with high pesticide residues linked with poor semen quality," Harvard School of Public Health News Press Release, March 31, 2015. You can read the entire article at http://www.hsph.harvard.edu/news/press-releases/ eating-fruits-and-vegetables-with-high-pesticide-residues-linkedwith- poor-semen-quality/ "The researchers used data from 155 men... at a fertility center in Boston. Data included 338 semen samples provided during 2007- 2012 and validated survey information about participants' diets. The researchers classified fruits and vegetables according to whether they contained high amounts of pesticide residues (such as peppers, spinach, strawberries, apples, and pears) or low-to moderate amounts (such as peas, beans, grapefruit, and onions). They then adjusted for factors such as smoking and body mass index-both known to affect sperm quality-and looked for connections between the men's intake of produce with pesticide residue and the quality of their sperm. The results showed that men who ate greater amounts of fruits and vegetables with higher levels of pesticide residue-more than 1.5 servings per day-had 49% lower sperm count and 32% lower percentage of normal sperm than men who ate the least amounts (less than 0.5 serving per day)."
What was the variable in this study