Smoking and heart attacks A Reuters story (April 2, 2003)

reported that “The number of heart attack victims fell by almost 60% at one hospital six months after a smoke-free ordinance went into effect in the area (Helena, Montana), a study showed, reinforcing concerns about second-hand smoke.” The number of hospital admissions for heart attack dropped from just under seven per month to four a month during the six months after the smoking ban.

a. Did this story describe an experiment or an observational study?

b. In the context of this study, describe how you could explain to someone who has never studied statistics that association does not imply causation. For instance, give a potential reason that could explain this association.