This chapter introduces the different kinds of studies commonly
used in medical research. Because we believe that knowing how a
study is designed is important for understanding the conclusions
that can be drawn from it, we have chosen to devote considerable
attention to the topic of study designs.
If you are familiar with the medical literature, you will recognize
many of the terms used to describe different study designs. If you
are just beginning to read the literature, you should not be dismayed
by all the new terminology; there will be ample opportunity to review
and become familiar with it. Also, the glossary at the end of the
book defines the terms we use here. In the final chapter of this
book, study designs are reviewed within the context of reading journal
articles, and pointers are given on how to look for possible biases
that can occur in medical studies. Bias can be due to the manner
in which patients are selected, data are collected and analyzed,
or conclusions are drawn.
There are several different schemes for classifying study designs.
We have adopted one that divides studies into those in which the
subjects were merely observed, sometimes called observational
studies, and those in which some intervention was performed,
generally called experiments. This
approach is simple and reflects the sequence an investigation sometimes
takes. With a little practice, you should be able to read medical
articles and classify studies according to the outline in Table
2–1 with little difficulty.
Table 2–1. Classification
of Study Designs. |Favorite Table|Download (.pdf)
Table 2–1. Classification
of Study Designs.
|I. Observational studies|
|A. Descriptive or case–series|
|B. Case–control studies (retrospective)|
|1. Causes and incidence of disease|
|2. Identification of risk factors|
|C. Cross-sectional studies, ...|
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