Designing and Running a Clinical Trial
Trevor F. Cox in Medical Statistics for Cancer Studies, 2022
A cohort study is a prospective study, where subjects are selected according to some criteria, and then followed for a period of time to establish who succumbs to the disease in question. For example, a group of people are selected, some of whom smoke and others do not, and during the next twenty years records are kept of who develop lung cancer and who do not. One problem with this is that you have to wait twenty years! A retrospective study can use data that was collected in the past and this will give a much speedier result. For example, patients needing frequent repeat interventions for chronic lymphocytic leukaemia (CLL) are selected from hospital records. Then their medical notes are scrutinised from the start of their treatment until ten years later, in order to map the progress of the disease. Other examples are given in Figure 4.1.
Epidemiology and its uses
Liam J. Donaldson, Paul D. Rutter in Donaldsons' Essential Public Health, 2017
The cohort study is a type of epidemiological investigation in which a population apparently free of the disease under study is assembled and each individual is categorized according to whether he or she has been exposed to the risk factor(s) of interest. The cohort is then followed up to see whether individual members of it develop the disease under study (or other diseases, in some cases). Comparisons are then made between the occurrence of the disease in the exposed and the nonexposed groups within the cohort. If the intention is to test the hypothesis that smoking causes lung cancer, the initial step is to classify the study cohort into smokers and nonsmokers. The cohort is then followed up over time, and cases of lung cancer are detected as they occur. The results are analysed to show what proportion of the smokers developed lung cancer compared with the proportion of nonsmokers.
A Review of Epidemiologic Studies with Regard to Routes of Exposure to Toxicants
Rhoda G. M. Wang, James B. Knaak, Howard I. Maibach in Health Risk Assessment, 2017
Briefly, the advantages of cohort studies relate to the ability to examine several disease outcomes, the occurrence of exposure to presumed etiologic factors prior to the development of overt disease (and hence the possibility of a causal relationship), and the better characterization of exposure information. Disadvantages relate to the cost involved, reflecting the large numbers of exposed and unexposed that must be followed to accrue sufficient numbers of rare events, and the long follow-up. Another problem concerns changes in exposure status during the follow-up period. Rarely, such changes can be monitored and adjusted for thorough analytic procedures, as in the case of uranium miners. Case-control studies can have greater statistical power with smaller sample sizes, and can be conducted in a shorter time period at lower costs than cohort studies.
The Florida Cohort study: methodology, initial findings and lessons learned from a multisite cohort of people living with HIV in Florida
Published in AIDS Care, 2021
Gladys E. Ibañez, Zhi Zhou, Christa L. Cook, Tania A. Slade, Charurut Somboonwit, Jaime Morano, Jeffrey Harman, Kendall Bryant, Nicole Ennis Whitehead, Babette Brumback, Angel B. Algarin, Emma C. Spencer, Robert L. Cook
Prior to this study’s initiation, there had been no large cohort studies focusing on PLWH in Florida. Cohort studies allow researchers to understand what happens to persons over time, and to identify strategies to improve health outcomes. The Florida Cohort research team, comprised of investigators and clinicians from several Florida universities and the Florida Department of Health (FDOH), sought to create a cohort that would span the entire state of Florida and reflect the unique demographic characteristics of PLWH. The Florida Cohort recruited primarily from public health settings, in order to engage a population which typically has less access to healthcare. Employing a socio-ecological conceptual model, the research team hypothesized that variables affecting the HIV care continuum would reflect the individual (e.g., attitudes, substance use, mental health), society (e.g., social support, stigma), and healthcare system (e.g., insurance, access to care, types of provider). Alcohol consumption was a focus of the cohort, because it is common in PLWH and correlates with HIV care (Vagenas et al., 2015).
Contemporary management and treatment strategies for asthma during pregnancy
Published in Expert Review of Respiratory Medicine, 2021
Jennifer A. Namazy, Michael Schatz
Observational studies and registries can provide important findings in this population of patients. Observational studies rely on patients being treated or not treated with specific medications and comparing the incidence of adverse events between two or more groups based on medication exposure. These types of studies can include prospective, retrospective database and case-control studies. Each has their own advantages. Prospective cohort studies have the advantage of capturing actual exposure, evaluating multiple outcomes, capturing and controlling for potential confounders. The retrospective database cohort study has the advantage of a large sample size and capturing multiple outcomes. However, observational studies are more prone to bias and confounding [41]. According to Schatz et al., the most comprehensive approach would be to use all of these methods to study the safety of a specific medication during pregnancy, while also attempting to control for the underlying severity and control of the asthma itself.
Regression analysis of case-cohort studies in the presence of dependent interval censoring
Published in Journal of Applied Statistics, 2021
Mingyue Du, Qingning Zhou, Shishun Zhao, Jianguo Sun
As discussed in Sections 4 and 5, a type of studies that is similar to case-cohort studies is the case–control study and the key difference between the two is the generation of the subcohort. With the case-cohort design, the subcohort is sampled from all study subjects, while the case–control design samples the subcohort only from the subjects who do not experience the failure event of interest during the follow-up. It is apparent that the data structures under the two designs are different but on the other hand, the simulation study suggested that the proposed estimation approach seems to be valid too for the case–control design. A possible explanation for this is that the resulting data may carry similar information about the model and the regression parameters of interest given the low percentage of the event rate.
Related Knowledge Centers
- Epidemiology
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