SeriesAn overview of clinical research: the lay of the land
Section snippets
A taxonomy of clinical research
Analogous to biological taxonomy, a simple hierarchy can be used to categorise most studies (panel).9 To do so, however, the study design must be known. As in biology, anatomy dictates physiology. The anatomy of a study determines what it can and cannot do. A difficulty that readers encounter is that authors sometimes do not report the study type or provide sufficient detail to figure it out. A related problem is that authors sometimes incorrectly label the type of research done. Examples
Is the study design appropriate for the question?
Starting at the bottom of the research hierarchy, descriptive studies are often the first foray into a new area of medicine. Investigators do descriptive studies to describe the frequency, natural history, and possible determinants of a condition.14, 16, 17 The results of these studies show how many people develop a disease or condition over time, describe the characteristics of the disease and those affected, and generate hypotheses about the cause of the disease. These hypotheses can be
Confusing fractions
Identification and quantification of outcomes is the business of research. However, slippery terminology often complicates matters for investigators and readers alike. For example, the term rate (as in maternal mortality rate) has been misused in textbooks and journal articles for decades. Additionally, rate is often used interchangeably with proportions and ratios.14 Figure 3 presents a simple approach to classification of these common terms.
A ratio is a value obtained by dividing one number
Conclusion
Understanding what kind of study has been done is a prerequisite to thoughtful reading of research. Clinical research can be divided into experimental and observational; observational studies are further categorised into those with and without a comparison group. Only studies with comparison groups allow investigators to assess possible causal associations, a fact often forgotten or ignored. Dichotomous outcomes of studies should be reported as measures of association with confidence intervals;
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