In the 1960's, deaths from lung cancer skyrocketed. Doctors treating these patients noticed that most lung cancer sullerers also smoked. Scientists felt that the chemicals
in cigarette smoke in some way caused lung cancer. Studies were designed in which a
group of 1,000 rats (Group A) were exposed to cigarette smoke while another group of
1,000 rats (Group B) were not exposed to cigarette smoke. In every other way Group A
and Group B were treated the same. After 18 months, the number of rats in Group A that
suffered from lung cancer was much higher than the number of rats in Group B. At the
end of the study, scientists stated, "cigarette smoke increased the chances of contracting
lung cancer."
Doctors noticed that most of their lung cancer patients also smoked. This is an example
of
O a hypothesis
an observation
O a conclusion
O a controlled experiment