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PHC 6000: Cohort

Introduction to epidemiology: Cohort studies

QuestionAnswer
In cohort studies, what type of participants do you start the study with? Begin the sample with a "healthy cohort" of individuals without the outcome.
In what order are risk factors and outcomes determined in a cohort study? Start with exposure status, then compare subsequent disease experience in exposed vs. unexposed. Presence or absence of risk factor is determined before outcome occurs.
What are other names for cohort studies? Follow-up studies, incidence studies, panel studies, longitudinal studies, or prospective studies
What does a prospective study mean? Outcomes have not yet occurred as study begins
What does a retrospective study mean? Outcomes have already occurred as the study begins
What is the main difference between a prospective and retrospective study? Difference in when the outcome occurs; in a prospective study, the outcome hasn't occurred when the study begins
In which type of cohort study is information more complete and accurate? Prospective
Which type of cohort study is more useful for discontinued exposures? Retrospective
Which type of cohort study is more useful for emerging new exposures? Prospective
Which type of cohort study is less costly? Retrospective
Which type of cohort study is more costly? Prospective
Which type of cohort study has a shorter completion time? Retrospective
Which type of cohort study has a longer completion time? Prospective
What is the basic approach / overall methodology to cohort studies? Identify cohort(s), measure exposure, follow for development of outcome
What are some examples of cohorts? -General population (i.e., outcome = high incidence) -Special exposure groups (e.g., smokers, uranium miners, asbestos workers) -Special resource groups (e.g., students, clinicians) -Geographically or facility-defined groups (e.g., hospitals, an island
Should cohort members be susceptible to the outcome of interest? Yes. Before beginning the study, determine who is susceptible and who is immune to the outcome of interest
How can susceptibility of potential cohort members be determined prior to the beginning of the study? Diagnostic tests or medical histories
Only the exposed group should be free from the outcome at start of a cohort study. (T/F) False; both exposed and unexposed should be free form the outcome at start and eligible to develop it during the follow up
When selecting subjects for a cohort study, what should be considered in regards to the exposure? Type of exposure under investigation and frequency of the exposure in the population
For common exposures, what type of exposed group would be suitable? General population
For uncommon exposures, what type of exposed group would be suitable? Specialty clinics or groups. The general population would not be suitable because you would need a LOT of participants to catch enough outcomes.
Should unexposed and exposed groups in a cohort study be comparable? Yes; if the unexposed group is different from the exposed group in ways that can influence the outcome, the study can lead to false conclusions
What is the principle of choosing the unexposed group for a cohort study? To allow a fair comparison with the exposed group
From what population should the unexposed group be sampled from for cohort studies? Same (or comparable) source population as the exposed
To what extent should the exposed and unexposed groups of a cohort study be similar? The baseline characteristics of exposed persons should not differ systematically from those of unexposed persons, except for the exposure of interest
Should multiple comparison groups of unexposed subjects ever be used in a cohort study? Why or why not? Yes; multiple comparison groups of unexposed subjects chosen in different ways may reinforce the validity of findings
What is a single sample cohort study? Also called population-based cohort; exposure is unknown until after the first period of observation
In a one-sample cohort study, who are the internal controls? The nonexposed discovered after the first period of observation
When is a multi-sample cohort study useful? If everybody in the cohort is exposed (special exposure cohort such as workers in a harmful industry)
How is the non-exposed comparison group for multi-sample cohort study selected? Select people as similar as possible to the exposed cohort (e.g., income, age, gender, employment); may use available population incidence rates under certain circumstances if a comparison group cannot be found
If exposure status changes during a cohort study, should those subjects be excluded? No
Source of information is not important to accuracy of exposure assessment. (T/F) False
What are some valid means of determining exposure in a cohort study? -Questionnaires -Laboratory tests -Physical measurements -Medical records
What are some valid means of determining outcome in a cohort study? -Hospital data or physicians -Periodic examination and records -Self report of subjects -Mortality
How can mortality status be determined in a cohort study? -Medical records -Autopsy records -Death certificates -Physician records -Next-of-kin
How can self report of subjects be corroborated? By examining medical records for some participants
What outcome measures are calculated in cohort studies? -Risk in the exposed -Risk in the unexposed -Relative risk -Attributable risk (risk difference) -Attributable risk percent -Incidence rate in the exposed -Incidence rate in the unexposed -Rate ratio -Survival curves -Cox proportional hazard ratio
What is a fixed cohort? All participants are followed from a defined/fixed starting point to a defined/fixed end point
What is another name for a closed cohort? Fixed cohort
What is a closed cohort? All participants are followed from a defined/fixed starting point to a defined/fixed end point
What is another name for a fixed cohort? Closed cohort
In a closed cohort, new entries are allowed after follow-up. (T/F) False; once start follow-up, no entries are allowed
What is a dynamic cohort? Participants may enter the study at different times; takes into account censorship and those lost to follow-up
What is an open cohort? Participants may enter the study at different times; takes into account censorship and those lost to follow-up
What is another name for a dynamic cohort? Open cohort
What is another name for an open cohort? Dynamic cohort
Which type of cohort design accounts for the fact that people contribute different time durations to the study? Open/dynamic cohort
In an open cohort, how is the denominator calculated? Based on the actual person years that each person has contributed
What type of cohort studies are especially useful for monitoring drug effects? Ambidirectional
Created by: AlneciaPHS