Series on the Evaluation of Scientific Publications
Order ID 53003233773 Type Essay Writer Level Masters Style APA Sources/References 4 Perfect Number of Pages to Order 5-10 Pages
Series on the Evaluation of Scientific Publications
R E V I E W A RT I C L E
Study Design in Medical Research Part 2 of a Series on the Evaluation of Scientific Publications
Bernd Röhrig, Jean-Baptist du Prel, Maria Blettner
SUMMARY Background: The scientific value and informativeness of a medical study are determined to a major extent by the study design. Errors in study design cannot be corrected afterwards. Various aspects of study design are discussed in this article.
Methods: Six essential considerations in the planning and evaluation of medical research studies are presented and discussed in the light of selected scientific articles from the international literature as well as the authors’ own scientific expertise with regard to study design.
Results: The six main considerations for study design are the question to be answered, the study population, the unit of analysis, the type of study, the measuring technique, and the calculation of sample size.
Conclusions: This article is intended to give the reader guidance in evaluating the design of studies in medical research. This should enable the reader to categorize medical studies better and to assess their scientific quality more accurately.
Dtsch Arztebl Int 2009; 106(11): 184–9 DOI: 10.3238/arztebl.2009.0184
Key words: study design, quality, study, study type, measuring technique
Institut für Medizinische Biometrie, Epidemiologie und Informatik (IMBEI), Johannes Gutenberg-Universität Mainz: Dr. rer. nat. Röhrig, Prof. Dr. rer. nat. Maria Blettner
Zentrum Präventive Pädiatrie, Zentrum für Kinder- und Jugendmedizin, Johannes Gutenberg-Universität Mainz: Dr. med. du Prel, M.P.H
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M E D I C I N E
and possibly that new hypotheses are generated. The following questions are important: Why? Who? What? How? When? Where? How many? The question to be answered also implies the target group and should therefore be very precisely formulated. For ex- ample, the question should not be “What is the quality of life?”, but must specify the group of patients (e.g. age), the area (e.g. Germany), the disease (e.g. mam- mary carcinoma), the condition (e.g. tumor stage 3), perhaps also the intervention (e.g. after surgery), and what endpoint (in this case, quality of life) is to be de- termined with which method (e.g. the EORTC QLQ- C30 questionnaire) at what point in time. Scientific questions are often not only purely descriptive, but also include comparisons, for example, between two groups, or before and after the intervention. For example, it may be interesting to compare the quality of life of breast cancer patients with women of the same age without cancer.
The research worker specifies the question to be an- swered, and whether the study is to be evaluated in a descriptive, exploratory or confirmatory manner. Whereas in a descriptive study the units of analysis are to be described by the recorded variables (e.g. blood parameters or diagnosis), the aim in an explor- atory analysis is to recognize connections between variables, to evaluate these and to formulate new hypotheses. On the other hand, confirmatory analyses are planned to provide statistical proofs by testing specified study hypotheses.
The question to be answered also determines the type and extent of the data to be recorded. This specifies which data are to be recorded at which point in time. In this case, less is often more. Data irrelevant to the question(s) to be answered should not be collected for the moment. If too many variables are recorded at too many time points, this can lead to low participation rates, high dropout rates, and poor compliance from the volunteers. The experience is then that not all data are evaluated.
The question to be answered and the strategy for evaluation must be specified in the study protocol before the study is started.
Study population The question to be answered by the study implies that there is a target group for whom this is to be clarified. Nevertheless, the research worker is not primarily interested in the observed study population, but in whether the results can be transferred to the target population. Accordingly, statistical test procedures must be used to generalize the results from the sample for the whole population (figure 1).
The sample can be highly representative of the study population if it is properly selected. This can be attained with defined and selective inclusion and exclusion criteria, such as sex, age, and tumor stage. Study participants may be selected randomly, for example, by random selection through the residents’ registration office, or consecutively, for example,
all patients in a clinical department in the course of one year.
With a selective sample, a statement can only be made about a population corresponding to these selec- tion criteria. The possibility of generalizing the results may, for example, be greatly influenced by whether the patients come from a specialist practice, a special- ized hospital department or from several different practices.
The possibility of generalization may also be influ- enced by the decision to perform the study at a single institution or site, or at several (multicenter study). The advantages of a multicenter study are that the required number of patients can be reached within a shorter period and that the results can more readily be generalized, as they are from different treatment centers. This raises the external validity.
Type of study Before the study type is specified, the research worker must be clear about the category of research. There is a distinction in principle between research on primary data and research on secondary data.
Research on primary data means performing the actual scientific studies, recording the primary study data. This is intended to answer scientific questions and to gain new knowledge.
In contrast, research on secondary results involves the analysis of studies which have already been per- formed and published. This may include (renewed) analysis of recorded data, perhaps from a register, from population statistics, or from studies. Another objective may be to win a comprehensive overview of the current state of research and to come to appropriate conclusions. In secondary data research, a distinction is made between narrative reviews, systematic reviews, and meta-analyses.
The underlying question to be answered also influ- ences the selection of the type of study. In primary research, experimental, clinical and epidemiological research are distinguished.
Experimental research includes applied studies, such as animal experiments, cell studies, biochemical and physiological investigations, and studies on
FIGURE 1 Connection between overall population and study population/data
186 Deutsches Ärzteblatt International⏐⏐Dtsch Arztebl Int 2009; 106(11): 184–9
Series on the Evaluation of Scientific Publications
QUALITY OF RESPONSE NO RESPONSE POOR / UNSATISFACTORY SATISFACTORY GOOD EXCELLENT Content (worth a maximum of 50% of the total points) Zero points: Student failed to submit the final paper. 20 points out of 50: The essay illustrates poor understanding of the relevant material by failing to address or incorrectly addressing the relevant content; failing to identify or inaccurately explaining/defining key concepts/ideas; ignoring or incorrectly explaining key points/claims and the reasoning behind them; and/or incorrectly or inappropriately using terminology; and elements of the response are lacking. 30 points out of 50: The essay illustrates a rudimentary understanding of the relevant material by mentioning but not full explaining the relevant content; identifying some of the key concepts/ideas though failing to fully or accurately explain many of them; using terminology, though sometimes inaccurately or inappropriately; and/or incorporating some key claims/points but failing to explain the reasoning behind them or doing so inaccurately. Elements of the required response may also be lacking. 40 points out of 50: The essay illustrates solid understanding of the relevant material by correctly addressing most of the relevant content; identifying and explaining most of the key concepts/ideas; using correct terminology; explaining the reasoning behind most of the key points/claims; and/or where necessary or useful, substantiating some points with accurate examples. The answer is complete. 50 points: The essay illustrates exemplary understanding of the relevant material by thoroughly and correctly addressing the relevant content; identifying and explaining all of the key concepts/ideas; using correct terminology explaining the reasoning behind key points/claims and substantiating, as necessary/useful, points with several accurate and illuminating examples. No aspects of the required answer are missing. Use of Sources (worth a maximum of 20% of the total points). Zero points: Student failed to include citations and/or references. Or the student failed to submit a final paper. 5 out 20 points: Sources are seldom cited to support statements and/or format of citations are not recognizable as APA 6th Edition format. There are major errors in the formation of the references and citations. And/or there is a major reliance on highly questionable. The Student fails to provide an adequate synthesis of research collected for the paper. 10 out 20 points: References to scholarly sources are occasionally given; many statements seem unsubstantiated. Frequent errors in APA 6th Edition format, leaving the reader confused about the source of the information. There are significant errors of the formation in the references and citations. And/or there is a significant use of highly questionable sources. 15 out 20 points: Credible Scholarly sources are used effectively support claims and are, for the most part, clear and fairly represented. APA 6th Edition is used with only a few minor errors. There are minor errors in reference and/or citations. And/or there is some use of questionable sources. 20 points: Credible scholarly sources are used to give compelling evidence to support claims and are clearly and fairly represented. APA 6th Edition format is used accurately and consistently. The student uses above the maximum required references in the development of the assignment. Grammar (worth maximum of 20% of total points) Zero points: Student failed to submit the final paper. 5 points out of 20: The paper does not communicate ideas/points clearly due to inappropriate use of terminology and vague language; thoughts and sentences are disjointed or incomprehensible; organization lacking; and/or numerous grammatical, spelling/punctuation errors 10 points out 20: The paper is often unclear and difficult to follow due to some inappropriate terminology and/or vague language; ideas may be fragmented, wandering and/or repetitive; poor organization; and/or some grammatical, spelling, punctuation errors 15 points out of 20: The paper is mostly clear as a result of appropriate use of terminology and minimal vagueness; no tangents and no repetition; fairly good organization; almost perfect grammar, spelling, punctuation, and word usage. 20 points: The paper is clear, concise, and a pleasure to read as a result of appropriate and precise use of terminology; total coherence of thoughts and presentation and logical organization; and the essay is error free. Structure of the Paper (worth 10% of total points) Zero points: Student failed to submit the final paper. 3 points out of 10: Student needs to develop better formatting skills. The paper omits significant structural elements required for and APA 6th edition paper. Formatting of the paper has major flaws. The paper does not conform to APA 6th edition requirements whatsoever. 5 points out of 10: Appearance of final paper demonstrates the student’s limited ability to format the paper. There are significant errors in formatting and/or the total omission of major components of an APA 6th edition paper. They can include the omission of the cover page, abstract, and page numbers. Additionally the page has major formatting issues with spacing or paragraph formation. Font size might not conform to size requirements. The student also significantly writes too large or too short of and paper 7 points out of 10: Research paper presents an above-average use of formatting skills. The paper has slight errors within the paper. This can include small errors or omissions with the cover page, abstract, page number, and headers. There could be also slight formatting issues with the document spacing or the font Additionally the paper might slightly exceed or undershoot the specific number of required written pages for the assignment. 10 points: Student provides a high-caliber, formatted paper. This includes an APA 6th edition cover page, abstract, page number, headers and is double spaced in 12’ Times Roman Font. Additionally, the paper conforms to the specific number of required written pages and neither goes over or under the specified length of the paper.
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