Morton and co-authors wished to determine if parents who work around lead
 inadvertently increase the level of lead in their children's blood.  Previous studies
 suggested that lead dust is brought home on the parents' clothing and skin, and can get
 into the children's bloodstream when the dust is breathed in or eaten.  Lead accumulates in
 the blood, so over time even small amounts can build to dangerous levels.

 Laws have been passed to limit the lead in paint, pipes, and other objects likely to be
 found in the home because even very small particles can poison a child after prolonged
 exposure.  If workers do in fact bring lead into the home this way, then careful hygiene at
 the factory (showering, changing clothes and shoes, and shampooing hair before leaving
 work) could prevent the lead from contaminating the home.

 Seeking the Evidence

        For this case study, you will determine whether there is sufficient
        evidence that the children of workers in this battery factory have
        higher levels of lead in their blood than children whose parents
        do not work around lead.

 A difference in lead levels between Exposed and Control groups does not in itself prove
 that the parents' exposure caused the children's elevated lead levels.  Only carefully
 controlled experiments can answer such questions definitively.

 But a controlled experiment is obviously out of the question here, for how could we
 assign children to their parents?  Or force parents into certain occupations?  To make the
 most of this less-than-perfect (from an experimental perspective) situation, special care
 must be given to the design of the study.

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