a.the neighborhood in which the Exposed child
lives and
b.the age of the Exposed child.
So, for each child in the Exposed group, a "match" was chosen
from the same
neighborhood and age group, but care was taken that this childís
parents did not work
around lead. These children comprise the Control group.
Now, if differences in the lead levels are found between the Exposed
and Control groups,
we know that the difference cannot be due to differences in age
or neighborhood, since
both groups are similar in these characteristics.
Forming Matched Pairs
It is not easy to form matched pairs. Researchers must carefully
search for another child
of the same age in the same neighborhood, and the parents of
this matched child must
consent to allow their child to participate in the study.
Initially, this study began with 34
children in the Exposed group, but one child was dropped because
researchers couldnít
find a matched pair.
Record your answers to these questions:
1. Is this an observational or a controlled study? Why?
2. The authors identified Age and Neighborhood as potential confounding
variables.
Compare these two to your choices. Explain how these variable
could confound the
study.
3. By matching each Exposed child to a Control child, the
researchers can control for
Age and Neighborhood. In effect, instead of having
33 Exposed subjects plus 33
Control subjects (for a total of 66 subjects) the researchers
now have just 33 pairs.
Given the study design, what sort of evidence would be required
to convince you
that the worker's exposure to lead put their children at risk
for lead poisoning?