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.
Understanding research
Geraldine Lee-Treweek, Tom Heller, Hilary MacQueen, Julie Stone, Sue Spurr in Complementary and Alternative Medicine: Structures and Safeguards, 2020
Epidemiologists try to discover the causes of disease by looking at the whole population rather than individuals. Some of the most important health-related discoveries were made by epidemiological research: for instance, the links between smoking and lung cancer and cholera and dirty drinking water. The two most common types of study are the cohort study (sometimes called a prospective study) and the case–control study (or retrospective study). The cohort study involves two groups, one of which has been exposed to something that is thought to affect health (for example, second-hand or passive smoking or asbestos). The two groups are then followed to see whether they develop a particular disease (such as lung cancer). The case-control study uses the reverse approach: a group of people who have a particular disease (such as heart disease or lung cancer) are asked about previous exposures (for example, whether they smoke) and their answers are compared with those of a group of people who do not have the disease. It is important to realise that epidemiological studies can only reveal links between events and not causes.
The prevalence of depressive symptoms in high-performance athletes: a systematic review
Published in The Physician and Sportsmedicine, 2020
Leigh Golding, Rory Giles Gillingham, Nirmala Kanthi Panagodage Perera
Systematic reviews of level II studies represent level I of the NHMRC evidence hierarchy. Prospective cohort studies represent level II; pseudorandomized controlled trials, retrospective cohort studies, and case-control studies represent level III; cross-sectional studies or case series represent level IV; and anecdotal reports or expert opinions represent level V. Thus, the study methodology/design of a prospective cohort study is superior to a case series. As such, the findings of high-quality studies (e.g. level II) will be more likely to be representative of the sampled population, and the results of such studies may be more reliably applied to other populations (external validity). By contrast, the findings of a low-quality study (level IV) cannot be generalized because results are likely to be different from the actual effects of a population. Because of poor internal validity, reviews that include studies with low levels of evidence are likely to be biased. All studies included in this review were either prospective cohort studies (two studies, level II) or cross-sectional studies (fourteen studies, level IV) (Figure 2). Consequently, the evidence surmised in this review was restricted by the limitations of each included study.
Increased risk for dislocation after introduction of the Continuum cup system: lessons learnt from a cohort of 1,381 THRs after 1-year follow-up
Published in Acta Orthopaedica, 2020
Oskari A Pakarinen, Perttu S Neuvonen, Aleksi R P Reito, Antti P Eskelinen
We acknowledge a few weaknesses in this study. The retrospective study design may enable information bias in the data that we cannot control. Also, adjusting the right confounding factors is not easy and, even when using the DAG, it is just a subjective view. Moreover, we did not have data on the patients’ alcohol use or neurodegenerative disorders, which are known to affect the risk for dislocation (Espehaug et al. 1997, Gausden et al. 2018). Furthermore, because the study cohorts were not randomized, there is always a risk for selection bias. The follow-up period was also rather short, but the majority of dislocations occur within 1 year after surgery (Blom et al. 2008, Meek et al. 2008). In addition, most revisions for dislocation are also performed within 1 year of the primary operation (Hailer et al. 2012). Still, a longer follow-up period would have provided more specific information about the long-term incidence and consequences of dislocations. The strengths of this study are the comprehensive and consistent data from 1 high-volume center that enabled the specific analysis of perioperative factors, such as liners, as there were no differences between hospitals as confounding factors. Indeed, the investigation of the patients’ case records enabled a more exact identification of all the possible dislocations. A clinical cohort study has an obvious advantage over register studies when there is a need to find and to prove causality. The use of DAG also limits the selection bias resulting from a collider (Shrier and Platt 2008).
Trajectories of disability in activities of daily living in advanced cancer or respiratory disease: a systematic review
Published in Disability and Rehabilitation, 2022
Lucy Fettes, Josephine Neo, Stephen Ashford, Irene J. Higginson, Matthew Maddocks
A prospective cohort study is an effective and appropriate way to observe trajectories of ADL disability as it allows for as many variables as required to be studied in order to determine any association with the outcome and allow all relevant confounding variables to be rigorously collected [59]. The sample should accurately reflect advanced cancer or respiratory disease using appropriate inclusion criteria [59], and use of multiple sites helps to widen recruitment and generalizability, and small samples can be pooled for increased power [60–62]. It is important to be aware that the efficiency of a prospective cohort study increases as the incidence of a particular outcome increases [59], which means it is necessary to recruit participants who are at risk of functional loss. Gatekeeping of the more unwell or disabled participants by clinicians can be prevented by use of a trained research assistant to screen for eligible participants [63].
Related Knowledge Centers
- Epidemiology
- Longitudinal Study
- Psychological Research
- Randomized Controlled Trial
- Retrospective Cohort Study
- Cohort
- Pharmacy
- Nursing
- Hierarchy of Evidence
- Confounding