Exam 2 Flashcards
(88 cards)
Experimental vs. observational
Experimental= population based with participants randomly chosen and randomly assigned to either exposure or non-exposure Observational= population based with participants not randomly put in exposed or unexposed (they chose to or not to participate in the risk factor.
Definition of a cohort
Any designated group of persons who are followed over a period of time
Cohort study
- Determine exposed/non-exposed groups first, then follow them to determine risk.
- start with people free of disease
- usually applied to rare exposures
- most rigorous observational study
- also known as prospective, longitudinal, incidence, or follow-up studies.
Strengths of cohort
- good for rare exposures
- can evaluate multiple effects of exposure
- clear temporal relationship between exposure and disease
Weaknesses of cohort
- loss to follow up
- requires a large sample
- costly
Framingham study
- large, longitudinal cohort study in 1948
- investigated risk factors for CVD (first use of “risk factor”
- 1948- first cohort
- 1971- second generation cohort(orig. participants’ children and spouses)
- 1994- first Omni cohort
- 2002- third generation cohort
- 2003- second Omni cohort
Framingham study risk factors
- high blood pressure and cholesterol
- diabetes
- obesity and physical inactivity
- smoking
- blood triglyceride and HDL cholesterol levels
- age
- sex
- psychological issues
Open or dynamic cohort
Members come and go and eligibility changes over time
Defined by changeable characteristics like smoking or residence in certain area
Fixed cohort
Membership defined at outset and no new members are gained later. Loss to follow up may occur
Defined by an irrevocable event like serving in the military or surviving natural disaster.
Defining cohorts
- if population is selected before exposures are known they may investigate more than one exposure or outcome and it is a single-sample or population based study
- if exposed groups are selected at the start based on their exposure then they are likely focusing on one exposure (common for occupational studies)
Types of exposed populations
Occupational- like miners, nurses, etc.
clinical- groups undergoing a particular medical treatment
Lifestyle factors or conditions
Veterans of specific wars
Geographically defined areas
Time period defined by exposure experience
Determining exposure status
Exposed- should be disease free but susceptible to disease, representative of exposed population, defined carefully
Unexposed- should be disease free but susceptible to disease, representative of the general population, and from the same underlying population as exposed group
How exposure data is collected for cohorts
-pre existing records (less expensive but less detail)
- questionnaires, interviews (good info but possible recall bias)
Direct testing (physical exams, environmental sampling, etc. )
-biological sample banks
How outcome data is collected for cohorts
- active participation- medical exams, lab tests, questionnaires
- no active participation of cohort members- death certificates, disease registries, medical records
Internal comparison
Exposed vs. unexposed members of the same cohort
External comparison
Exposed members of one cohort vs. unexposed cohort from another study
General population comparison
Members of cohort vs. general population
Common in occupational studies
Healthy worker effect- those that are employed are often healthier than unemployed.
2x2 table
Disease(a). No disease(b)
Exposed (c)
Not exposed (d)
Risk difference
[a/(a+b)] - [c/(c+d)] also known as attributable risk
Relative risk
[a/(a+b)]/[c/(c+d)]
First part= risk among exposed
Second part= risk among non- exposed
Interpreting relative risk
<1 = risk of disease for exposed is less than the risk of disease for non exposed (protective)
=1 means that the risk of disease is equal among exposed and non exposed (null value)
> 1 = risk of disease for exposed is greater than risk of disease for non exposed.
95% CI interpretation
If it includes 1.0, it is not a statistically different association
If it doesn’t include 1.0, it is a statistically significant association
Case control study
A type of observational analytic study in which subjects are selected on the basis of whether they do (cases) or do not (controls) have a particular disease under study
Also known as retrospective because previous exposure is assessed after identifying cases and controls.
Strengths of case control studies
- good for rare diseases/outcomes
- can evaluate multiple risk factors for the same disease/ outcome