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61 Cards in this Set

  • Front
  • Back
independent variable
Variables that define study groups
dependent variable
Outcome measures of interest
Descriptive vs. Analytic studies
Descriptive: describe something
you observe and describe what you see

Analytic: manipulate something to study it
Observational study
simply observe the occurrence of the outcome among the determined study groups

No manipulation of group characteristics (no intervention)
--I'm not telling you to do anything, just look at what naturally occurs
manipulate exposures/group characteristics and follow study population for outcome of interest

must be PROSPECTIVE! you have influenced the population
for something to be causal, what is a key point?
the exposure or characteristic has to occur BEFORE the outcome
what are the 2 observational study types used for generating hypotheses?
Ecological Studies
Cross-sectional studies
please list the 4 observational studies
Ecological studies
Cross-sectional studies
Case-control studies
Cohort studies
please list interventional study
Randomized controlled clinical trials (RCCTs)
what are ecological studies
tells us about the population

examine characteristics (risks/exposures, the independent variables) of a sample of an entire population as well as the presence of an outcome of interest (cases/disease, the dependent variable(s)) in the same sample of the entire population
What are the advantages of ecological studies?
Generate hypotheses
Quick; easy; inexpensive
what do ecological studies measure?
outcome frequency (prevalence; incidence rates)
What are disadvantages of ecological studies
No temporal relationships  no causality
Cannot test hypotheses
Ecological fallacy
Late-look bias
What is the ecological fallacy?
tendency to over-interpret the findings of an ecological study and ascribe characteristics of the sample population to specific individuals in the population. For example, as an extension of what we looked at in slide #8, we might be tempted to say that women who consume more dietary fat are more likely to develop breast cancer

Seen in ecological studies
What is the late look bias?
Seen in ecological studies
What is a cross-sectional study?
Prevalence of disease and association of disease with risk factor(s) at one point in time
Can a cross-sectional study address causality?
can a cross-sectional study determine incidence?
do you know the temporal relationship between exposure and outcome in a a cross-sectional study?
so what does a cross-sectional study measure?
what are the advantages of a cross-sectional study
Can examine possible association between risk and outcome
Relatively quick & easy; inexpensive
Can generate hypotheses
what are the DISadvantages of a cross-sectional study
Cannot assess causation
Late-look bias
Not good for hypothesis testing
what do you use to test hypotheses about associations and possible causation btw exposure and outcome?
control groups
describe case-control studies
The study design begins with people with disease (cases, or outcome) and compares them to people without disease (controls, or outcome)
Can you measure incidence with case-control studies? what about prevalence?


Investigator determines the number of cases and the number of controls that will be compared
Disease is not just “naturally occurring in the study population
case-control studies occur in what time-frame?
can case-control studies asses many risk factors for a single disease?
can case-control studies examine temporal relationships btw exposure and outcome?
can case-control studies show causality?

because you see the exposure come before the outcome
What are the challenges of case-control studies
Selection of controls (matched controls, hospitalized vs. non-hospitalized, problem of "overmatching"-dilute the ability to detect changes)

Recall limitations

measurement of case-control studies?
proportions, OR (odds of exposure ratio)
Can use OR to estimate risk in certain circumstances … what are these circumstances? (see later slide)
disadvantages of case-control studies
Recall bias
Challenge of selecting appropriate controls
Cannot measure incidence or prevalence
advantages of case-control studies
Can test hypotheses and examine causality
Can look at many risks for one disease
Relatively short; less expensive
Can more easily study conditions of low incidence or prevalence (good for studying rare diseases)
Which test is good for studying rare diseases?

case-control studies

don't have to wait for people to develop the disease, you just find those that have it
please describe cohort studies
Study groups are arranged based upon exposure status and then followed for development of the outcome
Outcome: disease incidence rates, mortality rates, etc.
Can evaluate incidence (unlike case-control studies)
Incidence rate is similar to risk (proportion of those exposed who develop disease)
can you measure incidence with cohort studies?
Are cohort studies prospective or retrospective?
Can be either!
is there randomization in cohort studies?
must know how to calculate odds and relative risk still
check out slide 29
when is odds ratio a good sign of relative risk?
when the disease does not occur frequently

this was on the last test
what do Cohort studies measure?
incidence rates and risks; relative risk
cohort study: retrospective or prospective?
Disadvantages of cohort prospective
time-consuming and costly; losses to follow-up; can study only the risk measured at the beginning of the study
Disadvantages of cohort Retrospective
recall limitations and bias
Disadvantages of cohort in general (both retro and pro)
Can only be used for common diseases
what are the advantages of cohort studies? main advantage?
Good at studying RARE RISK

Flexible: retrospective or prospective
Can use to determine actual measure of risk
Can study many disease outcomes
Good for studying rare risk factors
what is a Nested Case-Control Study?
Case-control study within a cohort study

(start with propective cohort study and take baseline measurements of characteristics. as the study moves forward through time cases develop as you are following them. as these cases develop, you match them with controls

cases and controls can be compared wtih respect to a variety of exposures

A way to enhance data collection and maximize cost-effectiveness in a prospective study
what do nested case control studies start with?
a prospective cohort study
what do interventional studies test?

what is the one example we have?

Clinical trials
What is the gold standard for studying interventions?
the RCCT (randomized control ed clinical trial)
What does the randomization do in the RCCT?
lowers the bias
can RCCT be retrospective?
shit naw
What is done to the exposure in RCCT? how is this different from other studies
In RCCT the exposure is manipulated

in other studies, things are just observed
RCFT (randomized controlled field trials) main goal is what? what bout RCCT?
RCFT focuses on preventive interventions

RCCT focuses on therapeutic interventions
what is a single blind study?
subjects do not know to which group they have been randomized
Group identity (experimental or non-experimental) is unknown

half get drug A, half get placebo

subjects don't know what they are getting
what is a double blind study?
both subjects and investigators are blinded to group identity

half get drug A, half get placebo

the experimenter and subjects dont know what group ppl are in
Stratification of group independent variables are ways of enhancing effects of randomization, how does it do this?
split up groups that could be potential confounders (take 1000 pts, can stratify by gender, age, etc)
what are the advantages of RCCT cross-over design?
increases the amount of data collected

allows for more comparisons between groups
measurement of RCCT?
incidence, prevalence, RR
disadvantages of RCCT? probably on the test
**External validity – can the results be effectively generalized to a broader population?

Most expensive and time consuming
Advantages of RCCT
Most scientifically rigorous

**Can be least subject to bias (double-blind studies)