Lecture 4 Flashcards
they observe the outcomes without intervening to affect them
observational studies
the reseacher manipilates the exposure (usually drug) to compare it to the standard of care
experimental studies
what kind of studies are ;
Cohort studies
case control studies
cross-sectional studies
observational studies
subjects are selected based on their exposure status
cohort study
__studies follow participants in time:
cohort
compares disease prevalence in the exposed and unexposed
prospective cohort
they begin with the exposure of interest and probe back for exposure information
retrospective cohort
maintains temporal sequence (assesses exposure before outcome)
good for assessing rare exposures and rapidly fatal diseases
can study multiple diseases/outcomes from a given exposure
advantages of cohort study
can calculate incidence among exposed and unexposed
cohort advantage
provides complete description of experience after exposure, including rate of progression and natural history of disease
cohort advantage
expensive
inefficient for rare diseases
long followup
disadvantage of cohort
cohort study selection of exposed - source depends on
research question
ability to collect exposure or diseased info
subjects are selected based on their diseased status
case-control study
theoretically should mimic cohort studies , diseased people are compared to non-diseased people
case-control study
in a case-control study, cases and controls should be different only on
their past exposure
can demonstrate risk indicators and not risk factors due to the retrospective nature of the study design (temporality cannot be assessed)
case-control study
the exposure has to be assessed retrospectively and the proportions of cases and controls who are exposed are unknown at the beginning of the study
case-control study
cases and controls must have an equal
chance of being exposed
efficient for rare diseases
relatively efficient in terms of time and money
can study diseases with long latency period
allow for the evaluation of multiple exposures that may increase risk for a specific disease
advantages of case-control studies
not optimal for rare exposures, cannot directly compute incidence of disease in exposed and non-exposed persons
temporal relationship cannot be established with certainty
prone to errors in selection of cases/controls and in errors pertaining to the collection of information
disadvantages case-control studies
case-control study: selection of \_\_; case (disease definition diagnostic criteria hospital based or population based incident or prevalent cases
selection of cases
case-control: selection of __;
would be cases if had the disease (similar to cases)
potential for bias and confounding
selection of controls
selection of subjects based on neither exposure or disease status
cross-sectional studies
most basic study design
“point-in-time” or snapshots information
subject selected without regards to exposure or disease status
does not need explained etiologic objectives
cross-sectional studies
sampling and analytic methods provide for statistically valid inference to populations
exposure and disease are assessed at the individual level
advantages of cross-sectional studies
temporality cannot be assessed
disadvantage of cross-sectional studies
randomized clinical trial
community intervention trials
experimental studies
principles of all experimental studies follow those from clinical trials
have a long history in clinical medicine
are sub-types of cohort studies in which exposure is randomly assigned by the investigator
randomized clinical trial
the process by which each participant’s treatment is determined by some random mechanism
randomization feature of RCT
the primary purpose of ___ is the minimizing of confounding
randomization
why randomize in RCT
to create groups that are not determined by any other factor than by chance
feature of RCT; the investigator and/or the participant do not know what arm the participant is in
blinding
the participant does not know but investigator does know treatment assignment
single blinded
neither the participant nor investigator know treatment assignment
double blindee
what is the purpose of blinding
to remove bias or systematic error
drawing different conclusions depending on their knowledge of which study arm particular participant is in
information bias
study recruiters can be eager to recruit “sick persons” into experimental arm
selection bias
key elements of\_\_\_; selection of study population allocation of treatment/intervention study conduct and compliance follow-up and establishing outcomes
RCT
considerations in experimental studies (3)
stopping rules, sample size, analysis and interpretation
systematic complete summary of the literature
systematic review
combined analysis of data from different studies following strict guidelines
meta-analysis
