Critical Appraisal of a Cohort Study

Published: 2018-02-04 23:02:38
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Cohort study critical appraisal

Research is a significant component in all professional fields and particularly in the health care sector. In the health care world, research forms the foundation of advancements and the number of studies done has continually been on the rise. This paper will critically examine the article by Rao et al. (2013) “Decreased Functional Status as a Risk Factor for Severe Clostridium difficile Infection among Hospitalized Older Adult.” Critical appraisal skill program (CASP), 2014 and Reader's guide to critical appraisal of cohort studies by Mamdani et al. (2005) will be applied in critiquing this article. The appraisal will delve into answering questions regarding whether the steps of the research process were conclusively followed. It includes the study design used, the sample size and data collection methods employed, ethical concerns and data analysis. This paper examines the limitations of the study, as well as the implications of the study findings on the medical fraternity. There is extensive information available in health care settings, which necessitates critical appraisal of the articles to separate low-quality research from resounding and relevant studies.

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The title of the article provides a description of what the study is about in a simple and concise manner. The title informs the reader of the aim of the study in an interesting way. A title should provide the summary of the content of the article and should be direct and straight to the point without any elements of ambiguity. Keywords lead the reader into understanding what the article is about and in this case they are the following: ‘decreased functional status,’ ‘risk factor,’ ‘geriatric,’ ‘Clostridium difficile,’ ‘infection,’ ‘aging,’ ‘colitis,’ and ‘hospitalized older adults.’

The principal purpose of an abstract is to explicate the purpose of the study, summarize the content in the paper and deliver the relevant elements of the article to the readers to get them interested in reading the article (Mamdani et al. 2005, p. 960).Within the abstract of this paper, the authors provided some background information about Clostridium difficile infection. Clostridium difficile is a bacterium that causes intestinal conditions such as pseudomembranous colitis and severe diarrhea. The most common cases of C. difficile occur in older adults within long-term care facilities or hospitals and normally occur after prolonged use of antibiotics. However, recent cases have been among individuals who are not considered a high-risk group including healthy young people and those who do not use antibiotics. Treatment of C. diff includes stopping the use of antibiotics, use of antibiotics to kill the bacteria and in severe or rare cases surgery may be required (Surawicz et al. 2013, p. 479). The prospective cohort study is the ideal study design, and the study setting is the University of Michigan Health System. The participants, measurements, results and the conclusion are also provided in the abstract. However, the abstract failed to state the purpose of the study concisely. The aims of any study should be in a non-technical and plain language so that the reader does not spend much time trying to discern what the study is about. Moreover, the researchers did not explicitly state the research questions, the hypothesis or the justification of the study. The rationale of the study is also not provided thus the reader will not understand why the study was important. The background of the study should be clear, and the researchers put the study into perspective and explain why the study is important. In this study, the researchers briefly introduced the topic but did not conclusively describe the concepts behind the study and little information was provided to give the study credibility. The researchers should have provided enough background information about the topic to help inform the aims and the method used in the study.

The literature review section was not clearly defined and it is obvious that the researchers did not provide anything for this section. There is a brief explanation under the introduction about the relationship between functional status and Clostridium difficile Infections and studies done on the same. The researchers failed to draw on the most recent, relevant, adequate evidence related to the research problem. They also did not summarize the variables and the relationship between variables. The study did not provide the theoretical framework of the study, and the key concept of the relevant literature was not well-defined.

Critical appraisal cohort study checklist: research design

In this study, a quantitative approach was employed, which is appropriate because of the need to quantify the problem and understand its prevalence. A quantitative approach permits the researcher to study the relationship between a dependent and an independent variable and uses the data to determine a cause-effect relationship, which is helpful in making predictions (Mamdani et al. 2005, p. 961). This was a study of 90 people aged 50 years and above and included hospitalized adults who had been diagnosed with diarrhea and had a positive C. difficile test. The potential research subjects were identified using microbiological records. The population size was adequate, but power analysis was not clearly stated to estimate the population size. The University of Michigan Health System, which is a 930-bed tertiary care, was the study setting.

The study used the cohort study design, which is also referred to as a longitudinal or follow-up study. In a cohort study, a population (which do not have a disease or outcome) are first divided into those exposed to a risk factor and those who are not. The exposed and unexposed subjects are followed for a period, usually long periods, and at the end of the period, the incidence of disease in the exposed group is compared to the incidence of the disease in the unexposed group (Mamdani et al. 2005, p.961). In the study, there was no mention of the unexposed group and the study subjects have already been tested positive for Clostridium difficile. If it were a cohort study, then after the study samples would be randomly selected. The individuals would be separated into those who exposed to the risk factor (in this case those with functional impairment) from the unexposed (those without functional impairment). The two groups would be followed for some time and observed if they developed Clostridium difficile infection (initially both groups are disease-free). The exposed group’s incidence rate is calculated then compared with the incidence in the unexposed group. A cohort study is very appropriate for this kind of research, but in this case, it was not well conceptualized and greatly misrepresented.

Cohort study critical appraisal tool: ethical concerns

Research involving human subjects raises significant ethical concerns. Therefore, universities, hospitals, and research institutions have put in place Research and Ethics Boards to ensure that the researchers uphold ethics during research. The research and ethics boards are put in place to protect both the researchers and the participants. The researchers obtained ethical approval from The University of Michigan Institutional Review Board. The research subjects in this study were vulnerable, and because of their illness, it was easier to enroll them into the study. In some cases, the researcher seeks consent from the consultant in charge in the hospital or the university’s Research and Ethics Board (REB) (Jeffrey et al. 2005, p.153). In this study, the authors stated that a written informed consent was given. Ethical principles reiterate on the importance of seeking informed consent from one’s research subjects before allowing them to participate in their studies (Mamdani et al. 2005, p.961). Ethical Stipulations also have it that research participants should not be coerced into participating in a study and are allowed to withdraw from the study at any given time.

Critical appraisal cohort study: sampling

The sampling method used in this study has not been clearly stated out. The information provided is that the research subjects were selected from electronic records, particularly with the help of microbiological records. Since there is no mention of random sampling, the study was prone to bias including selection bias thus the results may not be a true representation. Ideally, random error or bias, which is attributed to chance, does not necessarily affect the direction of the results but ultimately affects the precision of the results (Mamdani et al. 2005, p. 961). On the other hand, systemic errors, which result from the way the study is conducted affects both the direction of the results and precision of the study. The selection bias might interfere with the generalizability of the study. Moreover, the study does not provide any explanation regarding why the participants chose to participate in the study without any incentives. The research does not provide a comparison group in this case individuals who are not exposed to the risk factor, which makes the purported cohort study less reliable.

At no point does the paper mention any stratification that took place or any precautions put in place to deal with confounders or bias. The authors do not mention the potential biases that could most likely result from this study design or the researchers. For instance, loss to follow surrogate, or interviewer bias. The paper does not mention instances where the subjects dropped out of the study and how did they account for the losses. Moreover, there is no mention of potential biases from the information given by family members on behalf of the patients and the methods used to ensure that the information given was accurate. Since the patients were also interviewed, there was the possibility of recording recall bias and the authors must have mentioned how the bias was reduced within the study. According to CASP (2014), for research findings to be valid and reliable, bias should be reduced and it can including blinding the research subjects to ensure that the information about the research does not influence the responses provided.

Bias and confounding: data collection and analysis

The data collection in this study was carried out in some ways including a review of the medical records to obtain information regarding the patients’ clinical characteristics and microbiological test to determine the presence of C. difficile. More evidence on the functional status of the patients was obtained through interviews that were conducted with patients and their family members. There is no mention of where the interviews were conducted, but since it was on patients and their families, it is safe to infer that they were carried out within the health care facility. The paper was also very vague regarding the length of the interviews. Carrying out the interview at the health care center has several advantages including the calm and cool environment thus the interview will not be disturbed and in cases where the participants feel unwell, the health care professionals can step in to provide professional help. However, the interview might feel rather formal, which can easily make the respondent uncomfortable.

The paper mentioned that some of the information obtained through the interview include information regarding the patients’ ability to perform day-to-day activities including walking, bathing, grooming and feeding with assistance or independently. The baseline information was gathered before the patient was hospitalized and the onset of CDI. From the patients’ medical records, more information was gathered including intensive care unit admission, acute organ dysfunction, and immunosuppression. All the information gathered was useful for the study because it led to the establishment of the cause-effect relationship and answered the research question of the possibility of decreased functional status causing Clostridium Difficile Infection. To maximize the sensitivity of the study, the researchers combined the patient’s enrollment interviews and ICD-U code data. With this information, the authors provided a rationale for using this data collection method to ensure that there is validity in the whole process and the findings from the study. Some theories recommend that the researcher uses audio or video recording to sufficiently analyze the responses provided (Song et al. 2010, p.2334). The paper does not mention if the interviews were recorded and if the researchers depended on their memory, then it created loopholes for making mistakes.

The data was analyzed with the help of the severity score, which is a binary variable that recorded a positive relationship between severe CDI and diminished functional status. The functional status was characterized as full assistance where the patient needed help in all the daily activities, ‘some assistance’ where the patient needed assistance in some of the daily activity and ‘independent’ where the patient did not need any form of assistance. Univariate analysis was used in the study to identify the risk factors for a severity score that tested positive. During analysis of the results, a p-value of 0.05 or less was incorporated since it was considered statistically significant. The authors have extensively described the data analysis process and an in-depth description of the process was provided. Unfortunately, the data obtained through the interview also formed part of the independent variable and was statistically examined. The problem with this is the potential biases and confounding factors within the study design that were not measured or accounted for during the data analysis. The study fails to provide any data on the potential confounders and ultimately creates discrepancies in the results. Moreover, the calculation of odds ratio in a cohort study is not the best method of calculating the risk. Odds Ratio (OR) is appropriate in a case-control study (CDC, 2012; Holcomb et al. 2001, p.686). On the other hand, the Relative Risk would be more appropriate in the case of a cohort study. However, considering the misrepresentation of the study design right from the start, the authors failed to discern the most appropriate method of calculating the risk. Moreover, since the cohort study did not have a comparison group, the effect was estimated by the difference between the follow-up and baseline measures of the outcome and such estimates are vulnerable to bias and errors. The data presentation of the study was done well, but it would be more relevant if the authors accounted for any contradictory data.

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Critical Appraisal of a Cohort Study. (2018, Feb 04). Retrieved from


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