P.Mean >> Category >> Research design (created 2007-09-12).

These pages describe the variety of designs available to a researcher and contrasts their advantages and disadvantages. Also see Category: Observational studies, Category: Randomized trials. Other entries about research design can be found in the research design page at the StATS website.


5. What is a purposive sample? (September-Novmeber 2011)

Other resources:

Michael A Hussey, James P Hughes. Design and analysis of stepped wedge cluster randomized trials. Contemp Clin Trials. 2007;28(2):182-191. Abstract: "Cluster randomized trials (CRT) are often used to evaluate therapies or interventions in situations where individual randomization is not possible or not desirable for logistic, financial or ethical reasons. While a significant and rapidly growing body of literature exists on CRTs utilizing a "parallel" design (i.e. I clusters randomized to each treatment), only a few examples of CRTs using crossover designs have been described. In this article we discuss the design and analysis of a particular type of crossover CRT - the stepped wedge - and provide an example of its use." [Accessed September 1, 2010]. Available at: http://faculty.washington.edu/peterg/Vaccine2006/articles/HusseyHughes.2007.pdf.

Fernando Rico-Villademoros, Teresa Hernando, Juan-Luis Sanz, et al. The role of the clinical research coordinator - data manager - in oncology clinical trials. BMC Medical Research Methodology. 2004;4(1):6. Abstract: "BACKGROUND: The purpose of this study was to determine the standard tasks performed by clinical research coordinators (CRCs) in oncology clinical trials. METHODS: Forty-one CRCs were anonymously surveyed, using a four-page self-administered questionnaire focused on demographics, qualifications, and professional experience. The survey questions on responsibilities consisted of an ad-hoc 32-item questionnaire where respondents had to rate the frequency of involvement in the listed activities using a 3-point scale. We defined as "standard" a task that was rated as "in all or nearly all trials" by at least half of the respondents. RESULTS: A response rate of 90% (37 out of 41) was achieved after two mailings. Less than half of the respondents had received additional training in oncology, clinical research or Good Clinical Practices (GCP). Overall, all standard tasks performed by CRCs were in the category of "monitoring activities" (those usually performed by a Clinical Research Associate "CRA") and included patient registration/randomization, recruitment follow-up, case report form completion, collaboration with the CRA, serious adverse events reporting, handling of investigator files, and preparing the site for and/or attending audits. CONCLUSIONS: CRCs play a key role in the implementation of oncology clinical trials, which goes far beyond mere data collection and/or administrative support, and directly contributes to the gathering of good quality data." [Accessed September 1, 2010]. Available at: http://www.biomedcentral.com/1471-2288/4/6.

Journal article: Eduardo Mireles-Cabodevila, James K. Stoller. Research During Fellowship: Ten Commandments. Chest. 2009;135(5):1395 -1399. Excerpt: "Doing research is a critical component of an academic training experience for a fellow for at least four reasons, as follows: (1) the experience allows fellows to assess their interest in research and in its conduct as a core component of the career to follow; (2) the experience of doing research provides fellows with the opportunity for mentorship; (3) the research may jumpstart fellows' academic careers by initiating an area of content expertise, and allowing the beginning of a stream of inquiries and publications in that area1; and (4) the activities of doing research (eg, formulating hypotheses, presenting the research in various forums, writing grants, and submitting abstracts and [hopefully] manuscripts) offer the fellow practice in honing these skills in a mentored setting. Because doing good research is enhanced by experience, it behooves the fellow to harvest as many lessons (both do's and don'ts) from the training as possible. In this context, this article was written in the hope of both crystallizing and sharing lessons from a pulmonary/critical care fellow's research experience. Though eager to avoid the appearance of hubris in formulating these lessons as 'Ten Commandments,' we submit that framing this experience as commandments may lend the appropriate air of admonition to allow the reader to approach the experience as carefully as possible. " [Accessed on May 17, 2011]. Available at: http://chestjournal.chestpubs.org/content/135/5/1395.short

Celia Brown, Richard Lilford. The stepped wedge trial design: a systematic review. BMC Medical Research Methodology. 2006;6(1):54. Abstract: "BACKGROUND: Stepped wedge randomised trial designs involve sequential roll-out of an intervention to participants (individuals or clusters) over a number of time periods. By the end of the study, all participants will have received the intervention, although the order in which participants receive the intervention is determined at random. The design is particularly relevant where it is predicted that the intervention will do more good than harm (making a parallel design, in which certain participants do not receive the intervention unethical) and/or where, for logistical, practical or financial reasons, it is impossible to deliver the intervention simultaneously to all participants. Stepped wedge designs offer a number of opportunities for data analysis, particularly for modelling the effect of time on the effectiveness of an intervention. This paper presents a review of 12 studies (or protocols) that use (or plan to use) a stepped wedge design. One aim of the review is to highlight the potential for the stepped wedge design, given its infrequent use to date. METHODS: Comprehensive literature review of studies or protocols using a stepped wedge design. Data were extracted from the studies in three categories for subsequent consideration: study information (epidemiology, intervention, number of participants), reasons for using a stepped wedge design and methods of data analysis. RESULTS: The 12 studies included in this review describe evaluations of a wide range of interventions, across different diseases in different settings. However the stepped wedge design appears to have found a niche for evaluating interventions in developing countries, specifically those concerned with HIV. There were few consistent motivations for employing a stepped wedge design or methods of data analysis across studies. The methodological descriptions of stepped wedge studies, including methods of randomisation, sample size calculations and methods of analysis, are not always complete. CONCLUSION: While the stepped wedge design offers a number of opportunities for use in future evaluations, a more consistent approach to reporting and data analysis is required." [Accessed September 1, 2010]. Available at: http://www.biomedcentral.com/1471-2288/6/54.

Creative Commons License All of the material above this paragraph is licensed under a Creative Commons Attribution 3.0 United States License. This page was written by Steve Simon and was last modified on 2010-09-01. The material below this paragraph links to my old website, StATS. Although I wrote all of the material listed below, my ex-employer, Children's Mercy Hospital, has claimed copyright ownership of this material. The brief excerpts shown here are included under the fair use provisions of U.S. Copyright laws.


4. Stats: Enumerative and Analytic Studies (February 5, 2004). I received a question today via email about what statistics you can use when your sample equals the entire population. This issue also comes up when people ask about the use of the finite population correction factor. Both topics are controversial, and there is no clear consensus on what to do.


3. Stats: Web polls (July 30, 2001). Dear Professor Mean: I'm conducting a number of web-based polls on the web and would like to include a margin of error in my results. How do I do this?


2. Stats: Stratified random sample (August 23, 2000). Dear Professor Mean: What is a stratified random sample and why would I want to use one?

1. Stats: Quota stratified random sampling (January 28, 2000). Dear Professor Mean: I'm doing my thesis right now and I have to use the quota stratified random sampling. I do not know the exact meaning of this term.


Definition: Case-control design

Definition: Cohort design

Definition: Cross sectional design

Definition: Experimental design

Definition: Observational design

Stats: What is a purposive sample?

Definition: Quota sample

Definition: Retrospective Study

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