12 Study Designs
Statistics is more than just a collection of long columns of numbers and sets of
formulas. Statistics is a way of thinking—thinking about ways to gather and
analyze data. The gathering part comes before the analyzing part; the first
thing a statistician or a learner of statistics does when faced with data is to find
out how the data were collected. Not only does how we should analyze data
depend on how data were collected, but formulas and techniques may be mis-
used by a well-intentioned researcher simply because data were not collected
properly. In other cases, studies were inconclusive because they were poorly
planned and not enough data were collected to accomplish the goals and sup-
port the hypotheses.
Study data may be collected in many di¤erent ways. When we want infor-
mation, the most common approach is to conduct a survey in which subjects in
a sample are asked to express opinions on a variety of issues. For example, an
investigator surveyed several hundred students in grades 7 through 12 with a
set of questions asking the date of their last physical checkup and how often
they smoke cigarettes or drink alcohol.
The format of a survey is such that one can assume there is an identifiable,
existing parent population of subjects. We act as if the sample is obtained from
the parent population according to a carefully defined techinical procedure
calledrandom sampling. The basic steps and characteristics of a such a process
were described in detail in Section 3.1.2. However, in biomedical research, a
sample survey is not the common form of study; it may not be used at all.
The laboratory investigator uses animals in projects, but the animals are not
selected randomly from a large population of animals. The clinician, who is
attempting to describe the results obtained with a particular therapy, cannot
445
