Cohort Clinical Study
A Cohort Clinical Study is an Observational Clinical Study that is a Cohort-based Study in which risk measures are assessed, and the cohort is monitored for a long time period (i.e. years).
- Context:
- It can range from being a Retrospective Cohort Clinical Study to being a Prospective Cohort Clinical Study.
- It is aimed to assess the follwoing disease measures: point prevalence, period prevalence, and incidence.
- It is aimed to evaluted the following clinical risk measures: odds ratio, prevalence odds ratio, prevalence ratio, prevalence difference, attributable risk, incidence rate ratio, relative risk, and risk-hazard ratio.
- Strengths/Advantages:
- Temporality demonstrated;
- Individualized data;
- Ability to control for multiple confounders;
- Can assess multiple exposures;
- Can assess multiple outcomes.
- Weaknesses/Disadvantages:
- Expensive;
- Time intensive;
- Not good for rare diseases.
- Example(s):
- Counter-Example(s):,
- See: Case-Cohort Experiment, Matched-Control Quasi-Experiment, Cross-Sectional Study, Observational Study, Double-Blinded Clinical Trial, Disease Exposure Measure, Health Outcome Measure, Descriptive Clinical Trial, Diagnostic Clinical Trial, Interventional Clinical Trial, Panel Study.
References
2022
- (ClinicalTrials.gov, 2022) ⇒ https://clinicaltrials.gov/ct2/about-studies/glossary Retrieved:2022-02-13.
- QUOTE: Observational study model: The general design of the strategy for identifying and following up with participants during an observational study. Types of observational study models include cohort, case-control, case-only, case-cross-over, ecologic or community studies, family-based, and other.
2021a
- (Wikipedia, 2021) ⇒ https://en.wikipedia.org/wiki/Cohort_study Retrieved:2021-11-21.
- A cohort study is a particular form of longitudinal study that samples a cohort (a group of people who share a defining characteristic, typically those who experienced a common event in a selected period, such as birth or graduation), performing a cross-section at intervals through time. It is a type of panel study where the individuals in the panel share a common characteristic.
Cohort studies represent one of the fundamental designs of epidemiology which are used in research in the fields of medicine, nursing, psychology, social science, and in any field reliant on 'difficult to reach' answers that are based on evidence (statistics). In medicine for instance, while clinical trials are used primarily for assessing the safety of newly developed pharmaceuticals before they are approved for sale, epidemiological analysis on how risk factors affect the incidence of diseases is often used to identify the causes of diseases in the first place, and to help provide pre-clinical justification for the plausibility of protective factors (treatments).
- A cohort study is a particular form of longitudinal study that samples a cohort (a group of people who share a defining characteristic, typically those who experienced a common event in a selected period, such as birth or graduation), performing a cross-section at intervals through time. It is a type of panel study where the individuals in the panel share a common characteristic.
2021b
- (Wikipedia, 2021) ⇒ https://en.wikipedia.org/wiki/Glossary_of_clinical_research Retrieved:2021-11-21.
- Cohort study
- A research study that compares a particular outcome in groups of individuals who are alike in many ways but differ by a certain characteristic (for example, female nurses who smoke compared with those who do not smoke). (NCI)
- Cohort study
2017
- (Mathes & Pieper, 2017) ⇒ Tim Mathes, and Dawid Pieper (2017) ["Clarifying the distinction between case series and cohort studies in systematic reviews of comparative studies: potential impact on body of evidence and workload"]. In: BMC Medical Research Methodology, 17(107).
- QUOTE: Cohort study.
- A study in which a defined group of people (the cohort) is followed over time, to examine associations between different interventions received and subsequent outcomes.
- Case series.
- Observations are made on a series of individuals, usually all receiving the same intervention, before and after an intervention but with no control group.
- (...)
- Cohort study: Patients are sampled on the basis of exposure. The occurrence of outcomes is assessed during a specified follow-up period.
- Case series: Patients with a particular disease or disease-related outcome are sampled. Case series exist in 2 types:
- 1. Sampling is based on a specific outcome and presence of a specific exposure.
- 2. Selection is based only on a specific outcome, and data are collected on previous exposures. Cases are reported regardless of whether they have specific exposures. This type of case series can be seen as the case group from a case–control study.
- QUOTE: Cohort study.
2016
- (Grant, 2016) ⇒ William B. Grant (2016). "The role of geographical ecological studies in identifying diseases linked to UVB exposure and/or vitamin D". In: Dermato Endocrinology 8(1):e1137400. DOI:10.1080/19381980.2015.1137400.
- QUOTE: Observational studies come in several forms:
- Case–control. Risk-modifying factors measured at the time of disease diagnosis.
- Cohort and nested case–control. Subjects are enrolled in a study, risk-modifying factors are assessed, and then the cohort is monitored (for up to many years). Those who develop diseases are compared with like individuals who did not.
- Cross-sectional. An entire population is sampled, with health status and health parameters and risk-modifying factors measured.
- QUOTE: Observational studies come in several forms:
2014
- (Thiese, 2014) ⇒ Matthew S. Thiese. (2014). “Observational and Interventional Study Design Types; An Overview.” In: Biochemia Medica (Zagreb). Journal, 24(2).
- QUOTE: Cohort studies involve identifying study participants based on their exposure status and either following them through time to identify which participants develop the outcome(s) of interest, or look back at data that were created in the past, prior to the development of the outcome. Prospective cohort studies are considered the gold standard of observational research (...). These studies begin with a cross-sectional study to categorize exposure and identify cases at baseline. Disease-free participants are then followed and cases are measured as they develop. Retrospective cohort studies also begin with a cross-sectional study to categorize exposure and identify cases. Exposures are then measured based on records created at that time. Additionally, in an ideal retrospective cohort, case status is also tracked using historical data that were created at that point in time. Occupational groups, particularly those that have regular surveillance or certifications such as Commercial Truck Drivers, are particularly well positioned for retrospective cohort studies because records of both exposure and outcome are created as part of commercial and regulatory purposes (...). These types of studies have the ability to demonstrate temporality and therefore identify true risk factors, not associated factors, as can be done in other types of studies.
Cohort studies are the only observational study that can calculate incidence, both cumulative incidence and an incidence rate (...). Also, because the inception of a cohort study is identical to a cross-sectional study, both point prevalence and period prevalence can be calculated. There are many measures of risk that can be calculated from cohort study data. Again, the measures of risk for the exposure-outcome relationship that can be calculated in cross-sectional study design of odds ratio, prevalence odds ratio, prevalence ratio, and prevalence difference can be calculated in cohort studies as well. Measures of risk that leverage a cohort study’s ability to calculate incidence include incidence rate ratio, relative risk, risk ratio, and hazard ratio. These measures that demonstrate temporality are considered stronger measures for demonstrating causation and identification of risk factors.
- QUOTE: Cohort studies involve identifying study participants based on their exposure status and either following them through time to identify which participants develop the outcome(s) of interest, or look back at data that were created in the past, prior to the development of the outcome. Prospective cohort studies are considered the gold standard of observational research (...). These studies begin with a cross-sectional study to categorize exposure and identify cases at baseline. Disease-free participants are then followed and cases are measured as they develop. Retrospective cohort studies also begin with a cross-sectional study to categorize exposure and identify cases. Exposures are then measured based on records created at that time. Additionally, in an ideal retrospective cohort, case status is also tracked using historical data that were created at that point in time. Occupational groups, particularly those that have regular surveillance or certifications such as Commercial Truck Drivers, are particularly well positioned for retrospective cohort studies because records of both exposure and outcome are created as part of commercial and regulatory purposes (...). These types of studies have the ability to demonstrate temporality and therefore identify true risk factors, not associated factors, as can be done in other types of studies.
2005
- (Everitt & Howell, 2005) ⇒ Brian S. Everitt, and D. Howell. (2005). “Encyclopedia of Statistics in Behavioral Science." Wiley. ISBN:9780470860809
- QUOTE: In a controlled observational cohort study, two groups of subjects are selected from two populations that (hopefully) differ in only one characteristic at the start. The groups of subjects are studied for a specific period and contrasted at the end of the study period. For instance, smokers and nonsmokers are studied for a period of 10 years, and at the end the proportions of smokers and nonsmokers that died in that period are compared. On the other hand, in an intervention study, the subjects are selected from one population with a particular characteristic present; then, immediately after baseline, the total study group is split up into a group that receives the intervention and a group that does not receive that intervention (control group). The comparison of the outcomes of the two groups at the end of the study period is an evaluation of the intervention. For instance, smokers can be divided into those who will be subject to a smoking-cessation program and those who will not be motivated to stop smoking.[1]