Review of Part III
Review of Part III – Gathering Data
The researchers performed a prospective observational study, since the children were
identified at birth and examined at ages 8 and 20.
There were indications of behavioral
differences between the group of “preemies”, and the group of full-term babies.
“preemies” were less likely to engage in risky behaviors, like use of drugs and alcohol, teen
pregnancy, and conviction of crimes.
This may point to a link between premature birth
and behavior, but there may be lurking variables involved.
Without a controlled,
randomized, and replicated experiment, a cause-and-effect relationship cannot be
A retrospective observational study was performed.
There may be a link between tea
drinking and survival after a heart attack.
Other variables, like overall health and
education might also be involved.
Since lurking variables may be involved, a controlled,
randomized, and replicated experiment must be performed to determine whether or not a
cause-and-effect relationship exists between tea drinking and post heart attack survival.
The researchers at the Purina Pet Institute performed an experiment, matched by gender
The experiment had one factor (diet), at two levels (allowing the dogs to eat as
much as they want, or restricted diet), resulting in two treatments.
One of each pair of
similar puppies was randomly assigned to each treatment.
The response variable was
length of life.
The researchers were able to conclude that, on average, dogs with a lower-
calorie diet live longer.
The officials used a random sample.
The population is all homes on the property tax list.
The parameter of interest is level of radon contamination.
The officials’ procedure is not
clear, but if they make an effort to get some houses from each area in the city, the sample is
stratified by area.
If the procedure is followed carefully, the officials can use the results of
the sample to make inferences about the radon levels in other houses in the county.
It is not apparent whether or not the high folate intake was a randomly imposed treatment.
It is likely that the high folate intake was simply an observed trait in the women, so this is a
prospective observational study.
This study indicates that folate may help in reducing
colon cancer for those with family histories of the disease.
There may be other variables in
the diet and lifestyle of these women that accounted for the decreased risk of colon cancer,
so a cause-and-effect relationship cannot be inferred.
The research team performed a retrospective observational study.
There is evidence that
the date of first flowering has generally advanced over the last 47 years, but there may be
other variables besides climate change that can account for this.
The assertion of the
researchers is speculative.