Use the following article summary to MARK ALL CORRECT interpretations.

A New Zealand study published in 2012 in theProceedings of the National Academy of Sciences, followed 1,037 people from birth to age 38. Subjects had their intelligence quotient, or IQ, tested at ages 13 and 38, and were monitored for marijuana use throughout their lives. Subjects who began smoking pot as teenagers saw aneight-point IQ drop-offwhen they were tested again later in life. Interestingly, people who starting using pot as adults showed no decrease in IQ, while people who never used it at all actually saw their intelligence quotientsincrease from age 13 to 38.

Researchers considered that use of marijuana with the past 24 hour of the IQ test, other substance abuse or schizophrenia, etc. might account for the drop in IQ, so they used advanced statistical methods to control for those factors. Even so, they found IQ decline "remained statistically significant (t= -2.2, Pvalue = 0.0282)."

Select one or more:

a.The explanatory variable is marijuana use

b.Since the p-value is low, the link between using marijuana as teen and loss of IQ is NOT easily explained by chance alone.

c.Following subjects from birth allowed the researchers to guarantee that they had the same information for all subjects. For example, researchers administered IQ tests to all subjects at age 13.

d.The study was experimental rather than observational

e.The variable, IQ, is categorical

f.The study was retrospective