Stat 221 Introduction to Probability and Statistics Fall 2008
Quiz 3
Taken on Thur, Sept 25.
You may work with one partner, submitting one sheet with both names.
You want to investigate whether teenagers in
1) Identify the populations in this study.
The populations are all teenagers in
2) Identify the explanatory variable, and classify it as categorical or quantitative.
The explanatory variable is the
country that the teenager lives in. This
is a categorical variable.
3) Identify the response variable, and classify it as categorical or quantitative.
The response variable is the number
of Harry Potter books that the
teenager has read. This is a
quantitative variable.
In a study published in a 2007 issue of the journal Preventive Medicine, researchers found that smokers were more likely to have used candy cigarettes as children than non-smokers were. When hearing about this study, one person responded “But isn’t the smoking status of the person’s parents a confounding variable here?”
4, 5) Describe what it means to be a confounding variable in this context. Be sure to indicate how this potential confounding variable could be related both to the explanatory variable and the response variable.
It’s certainly possible, and it seems
fairly plausible, that children of smokers would be more likely to use candy
cigarettes than would children of non-smokers.
But in that case we cannot distinguish between the effects of the candy
cigarettes and the effects of parents’ smoking on whether the children grow up
to be smokers. It also seems plausible
to believe that children of smokers are more likely to smoke than children of
non-smokers, so the confounding variable (parents’ smoking status) is
associated with both the explanatory variable (use of candy cigarettes) and the
response variable (smoking status of children when they become adults).