Case Control Study Analysis Venous Thromboembolism

Questions: 1.Provide one paragraph of summary of the study youve chosen and I approved (200 words Max) in your OWN WORDS to show the reader (me) that you have understood the study and you everything about it because you read it few times.2. What is the research question? Provide the full version3. Was the study design appropriate and how else can it be done (give details of another alternative design in relation to the same objectives and study settings)?4. What are the comparison groups in this study? Were theysimilar to the cases? explain5. Are the study population representative of the general population? Explain your answer6. How were the control group selected? What do you think of that?7. What analytical strategy was used to assess results?8. What measures were used to assess the relationship between risk factor and outcome? Where these objective or subjective?9. What are the types of bias that may affect this study? Explain these specifically and in relation to the following:Study popula tion (think of the groups)Recruitment process (observation, objective or subjective, responder etc.)Measurements used andIssues related to the use of cases and control groups10. How do you think issues (Bias) in the previous question can influence the results (discuss this in details and in relation to the above)?11. Comment on external validity of the results12. How precise was the estimate of the effect or the assosciation?13. What confounders did the authors adjust for? In your opinion, couldhave there beenany other confounders in his study that could have influenced the results (i.e. the association between exposure and outcome)? Answers: 1. Venous Thromboembolism (VTE) is one of the major health issues prevalent in United States. Scientists attribute the reason behind not being able to reduce the incidence rate of the disease, to lack of known risk factors and consequently inability to identify the risk groups in the population. Heit et al. (2000), in their study aim to identify the independent risk factors related to deep vein thrombosis and pulmonary embolism (PE) and evaluate the magnitude of the individual risks as well. The authors seek to conduct this study as pervious researches on this issue did not have efficient study designs to encompass the whole spectrum of the disease. A case control study was conducted by utilising the data of Olmsted County residents from the Rochester Epidemiology Project, by applying certain selection and exclusion criteria. 625 patients of Olmsted County with first time VTE were selected as the study group and 625 patients without the condition as the control group. The authors fou nd surgegy, trauma, hospital or nursing home confinement, malignant neoplasm with or without chemotherapy, central venous catheter or pacemaker, superficial vein thrombosis and neurological disease with extreme paresis as independent risk factors. 2. The research question of the study: What are the independent risk factors associated with VTE and PE and the magnitude of the risk factors? 3. The study design followed is a case control study where the authors sample the population into diseased and non-diseased individuals from previous records and evaluate the association of VTE and PE with past exposures. Another study design that could have been utilized for the purpose of this study is a Cohort Study. In such a study disease free are sampled based on certain exposures and observed over time to identify who are affected by the disease of concern. It can measure new incidence of the disease and thus identify the risk factors based on which the samples were classified. 4. The comparison group in the study comprised of 625 Olmsted County patients who were not affected by VTE. The patients were similar in that they were sampled based on similar age, sex, calendar year and medical record number compared to that of the study group. 5. Yes the study population can be considered as representative of the general population as it was sampled using data recorded over a period of 15 years and patients were selected based on specific selection criteria of first lifetime VTE. 6. The control group was selected from the same data set, collected over the same time period, after matching for age (1 year), calendar year (1 year), sex and those with the closest medical record numbers. Hence, it can be considered that the control group efficient and eliminates the effects of time which are of pivotal importance especially for case control studies. 7. Initially several baseline characteristics were tested as risk factors. Data was collected from medical records of each patient. The baseline characteristics were analyzed based on both univariate and multivariate assumptions. More than 25 baseline characteristics were classified of being potential risk factors. 8. The assessment of baseline characteristics as being potential risk factors was done by conditional logistic regression method. The measures were objective as the data collected was recorded in the past over a period of 15 years. 9. The study may have several biases regarding different aspects. The Study and control groups selected were strictly from the Olmsted County and hence the results cannot be considered appropriate for a larger population as location related confounding factors may affect the same. No bias was found in the recruitment process as the authors avoided referral bias by selecting subjects on specific set of selection criteria which were efficient. However, attributes such as race and ethnicity were not considered that may have an influence on the incidence of the disease. The measurement used was objective as data was not collected directly from the patients and hence certain bias may prevail while recoding the data in the first place. The control groups were selected based on similar age, sex, calendar year and nearest medical record number and hence apart from the fact that other confounding factors may be present in both the groups there were no direct bias issues in the study group and the control group. 10. The results can be severely misleading if other confounding factors are present in the population that is related to the location of the study. In such cases the risk factors identified needs to be studied for prevalence discrepancies over different locations in order to extrapolate the findings beyond Olmsted County. 11. As already mentioned, as the study population was confined to a specific location, the external validity of the results cannot be evaluated efficiently. Further insight on the topic is required to estimate the application of the results over generalized population and location. 12.The estimates of the association can be considered precise as they were consistent with previous study findings and some risk factors even showed a greater association compared to previous study results. Association of the disease with hospital, nursing home or other care facility confinement was first identified in this study. 22-fold increased risk was found in patients hospitalized with a prior history of surgery, 13-fold increase for patients with trauma, 4-fold increase for patients with malignant neoplasm alone, and a 3-fold increase for patients with neurologic disorders and extremity paresis or plegia. 13. In case of confinement to hospital, nursing home or healthcare facility the authors considered the confounding factors of acuity and severity of the illness. The study was the first to identify current or recent central venous catheterization as an independent variable, which the authors considered as having the possibility of being a confounding factor for the disease. Additional confounding factors that should have been considered are environmental factors, race and ethnicity of the subjects of both the groups. References Heit, J.A., Silverstein, M.D., Mohr, D.N., Petterson, T.M., O'Fallon, W.M. and Melton, L.J., 2000. Risk factors for deep vein thrombosis and pulmonary embolism: a population-based case-control study.Archives of internal medicine,160(6), pp.809-815.