I followed with great interest the discussion about descriptive versus hypothesisdriven research (A. Casadevall and F. C. Fang, Microbe, December 2008, p. 552- 553, andMay2009, p. 207; J. L. Slonczewski and E. S. Kaneshiro, Microbe, February 2009, p. 50).  The authors talked about various ways of defining "descriptive research" and evaluated its value to science.

My understanding is that quantitative research is typically associated with hypothesis- driven, experimental approaches. An example is bench-level research in microbiology which is characterized by structured observation, hard data, control group, deductive approach, and use of statistical tools, among others. Another form of research is purely descriptive. The description of an observed phenomenon (e.g., the discovery of a microorganism in a particular environmental setting) without having an immediate explanation for its existence might qualify as an example.

In epidemiology, descriptive (or observational) research relates to different types of study designs (e.g., case reports and case series, ecologic and cross-sectional studies, as well as cohort and case-control studies), which are considered nonexperimental and noninterventional. This is in contrast to experimental study designs (e.g., clinical trials and time series). Another way to describe these study designs is by dividing them into descriptive studies (e.g., case reports, case series, and ecologic studies) and analytical studies (e.g., cross-sectional and cohort studies, case-control studies, and clinical trials). A common sequence in epidemiology research is clinical observations (i.e., recognizing a new or increased pattern of disease), descriptive studies (describing the distribution of disease and identifying clues for further investigation), and analytical studies (testing a specific hypothesis that Exposure A leads to Disease B) [J. L. Kelsey, A. S. Whittemore, A. S. Evans, and W. D. Thompson, Methods in observational epidemiology (2nd ed.), Oxford University Press, New York, NY, 1996; K. E. Nelson and C. M. Williams (ed.), Infectious disease epidemiology: theory and practice (2nd ed.), Jones and Bartlett Publishers, Boston, Mass., 2007].

In the social sciences (e.g., anthropology, sociology, and psychology), the umbrella term "qualitative" approach is used to refer to a research design that is evolving and flexible; it creates descriptive (soft and rich) data through observation (e.g., people's own words, field notes, and official documents/artifacts) and its analysis is ongoing and inductive, leading to the description of multiple realities, to understanding and meaning, and the development of sensitizing concepts. The qualitative research approach is aimed at examining the world with the assumption that "nothing is trivial, that everything has the potential of being a clue that might unlock a more comprehensive understanding of what is being studied" [R. C. Bogdan and S. K. Biklen, Qualitative research for education: an introduction to theories and methods (5th ed.), Pearson Education, Boston, Mass., 2007].

Finally, there is mixed-methods research. This approach uses both qualitative and quantitative methods and blends the resulting data in certain ways. An increasing number of scientists considers this type of research the most powerful of all. Investigators in various fields (including public health and education) and across professional disciplines have begun to use it in order to get a more holistic view on topics under study [e.g., L. Curry, R. Shield, and T. Wetle (ed.), Improving aging and public health research: qualitative and mixed methods, American Public Health Association, Washington, D.C., 2006; J. W. Creswell and V. L. P. Clark, Designing and conducting mixed methods research, Sage Publications, Thousand Oaks, Calif., 2007].

In conclusion, I believe there is not one single method that is inferior to another. In this sense, I agree with Casadevall and Fang as well as with Slonczewski and Kaneshiro that "descriptive research can illuminate novel phenomena or give rise to novel hypotheses" and that we should "avoid privileging one mode of discovery over another," respectively. I believe that the choice of research design solely depends on the kind of question an investigator wants to answer. On a final note: My presentation here of information about different types of research approaches is essentially descriptive-nevertheless, I hope it will shed some more light on the terminology of various research designs used to advance our understanding of the world in which we live.

Christian T. K.-H. Stadtländer University of St. Thomas
Minneapolis-St. Paul, Minn.

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