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COPYRIGHT 2003 Jannetti Publications, Inc.
This is part two of the discussion on research design. Part one (Colling, 2003a) covered common types of study designs for quantitative and qualitative studies and a discussion about the study setting. Prior articles included defining a research problem and the important aspects of a literature review (Colling, 2003b, 2003c). In this article, sample selection and determining the number of subjects needed for the study will be addressed. In addition, two other components of the design section of the study will be discussed: the intervention (for a clinical trials study) and the procedures. The final part of the design, how to plan to measure attributes within the study question, will be covered in part three of this series (February 2004). Future articles will include material on collecting and analyzing data, where to find money to conduct the study, how to write a budget, and finally how to write up the findings from the study and disseminate study results.
The decision points along the research journey are like crossroads in highways. They require thought and study to make the best decisions in order to reach your destination. Some decisions may lead to a smoother journey while others to a more tangled journey and unclear destination. Mapping the entire route (design) prior to beginning your research journey will take more time and planning but will increase the strength of the study and get you to your goal more quickly.
Sample Selection
Studies rarely gather information from an entire population of interest. Instead, a sample is selected. Sampling saves time and expense. A major concern in selecting a sample is how representative the sample is to the population; that is, how closely does the sample mirror the characteristics of the entire population of interest. While books have been written on sample selection, several common sampling strategies are presented in Table 1.
Convenience sample. This type of sampling is easy and usually inexpensive. It is a weak strategy to use, however, unless no other alternatives are possible or you are doing a pilot study (a small preliminary study prior to conducting a larger study). The researcher has no control over the characteristics of the sample which may mean the sample may be quite different from the...
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