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PHC 6000: Cohort
Introduction to epidemiology: Cohort studies
| Question | Answer |
|---|---|
| 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
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