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Epi Exam 2 > Epidemiologic study design > Flashcards

Epidemiologic study design Flashcards

1
Q

What are the 3 descriptive studies?

A

Case reports
Case series
Cross-sectional

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2
Q

What are the 6 Analytic studies?

A 
Ecological
Cross sectional
Case control
Cohort
Experimental
Meta-analysis
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3
Q

What are the two main kinds of analytic studies?

A

Experimental

Observational

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4
Q

What is the major difference b/w experimental vs observational analytic studies?

A

experimental tx or exposure is allocated/asigned to subjects

observational subjects select their own exposure

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5
Q

Validity of experimental studies rests on two important criteria, what are they?

A
  1. validity of comparison

2. validity of measurement

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6
Q

What error is it called when there is a lack of comparability b/w study groups?

A

confounder

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7
Q

What error is it called when collected information is not accurate?

A

Information bias

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8
Q

How do we best approach a valid comparison during an experimental study?

A

Randomization is the best way to achieve comparability b/w tx groups

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9
Q

What is random sampling? What is randomization?

A

Random sampling – randomly choosing a sample

Randomization – randomly allocating groups from the sample to tx or other aspect of the study

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10
Q

What is the key feature of randomization?

A

One individual is no more or less likely to receive a particular tx than any other individual in the study population

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11
Q

T/F

Randomization is a guarantee for making groups equal

A

False

It is not guaranteed

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12
Q

What is blinding?

A

Principle where whoever measures the outcomes in the study subjects be unaware of what the tx assignment was - this way they cannot be influenced (biased) by knowing which group the study subjects are in

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13
Q

What are three advantages of experiments?

A
  1. Best way to produce evidence for causal effect
  2. May be the only practical way to study certain clinical problems
  3. Can sometimes lead to faster results than observational studies
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14
Q

What are 4 disadvantages to experiments?

A
  1. Costly in time and money
  2. may be ethical problems
  3. may be lack of variation in participants
  4. non-compliances and dropouts
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15
Q

What are the 4 main types of observational studies?

What is unique about these observational studies compared to experimental?

A
  1. Ecological
  2. Case-control
  3. Cohort
  4. Cross-sectional

Researcher doesn’t control circumstances leading to exposure

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16
Q

When is an ecological study done?

A

When information is known on entire groups, not on individuals

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17
Q

What are cross sectional studies?

A

Comparison b/w groups
No follow up!
Study dz and exposure status at one point in time
Cannot measure incidence (risk, rates) of dz – only prevalence
Cannot always know if exposure preceded dz or followed it

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18
Q

What does it mean if a sample is longitudinal?

A

They are being followed up

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19
Q

What are cohort studies?

A

Longitudinal study
Group of individuals at risk are followed up
Some of the cohort members are exposed, some are not
Can measure either cumulative incidence (risk) or incidence rates

20
Q

What is the definition of Cohort?

A

An assemblage of individuals who are at risk of the dz (outcome) and who share certain characteristics in common

21
Q

Cohort studies can be ______ or _____________

A

Prospective or Retrospective

22
Q

What is the difference b/w prospective and retrospective?

A

Prospective: assemble cohort at time study begins and follow individuals forward and measure dz occurrence and calculate risks/rates

Retrospective: obtain historic exposure and outcome information on a cohort that was assembled sometime in the past

23
Q

When are cohort design studies useful?

A

Disease is common, exposure is rare, or you wish to study multiple outcomes

24
Q

What are 2 major cohort design issues?

A
  1. Expensive

2. Reason an individual leaves a cohort is related at all to the outcome = bias may result

25
Q

What is this phenomenon called… Reason an individual leaves a cohort is related at all to the outcome = bias may result?

A

Censoring or lost to follow up

26
Q

T/F

It is a great idea to do a cohort study on a rare dz

A

False

27
Q

What is another kind of cohort study?

A

Case control

28
Q

How is a case control study different than a cohort?

A

Sample them based on their disease status, not their similar exposures
The cases are taken from disease registries, hospital records, vet records, etc.

29
Q

When do you use a case control study over a cohort study?

A

When the disease is rare

30
Q

What does the control in a case control study look like?

A

Non-diseased individual

31
Q

What can’t we calculate from a case control study? Why?

A

risk
risk difference
ratios

The choice of the number of controls is arbitrary

32
Q

What do investigators calculate from a case control study?

A

Exposure odds ratio

33
Q

How do you calculate an exposure odds ratio?

A

Probability of exposure in the cases / probability of exposure in non-cases

(Cases exposed/cases unxposed) / (non-cases exposed/ non-cases unexposed)

34
Q

Can exposure odds ratio be used for causal inferences? If no, what can?

A

No

Disease odds ratio

35
Q

How do you calculate disease odds ratio?

A

(cases exposed/non-cases exposed) / (cases unexposed/noncases unexposed)

36
Q

What are the three main rules for case-control studies?

A
  1. control should only be selected if someday, if it were to become a case, it can be eligible to become a case we are studying
  2. Controls should be selected for reasons that are unrelated to the exposure studied
  3. Select incident cases, not prevalent ones
37
Q

What are 5 issues with a case-control study?

A
  1. Relatively inexpensive compared to experimental and cohort studies
  2. If it is performed retrospectively, the duration may be short if we can easily retrieve info
  3. Ideally suited to examine a large number of population risk factors
  4. Often no way to verify accuracy (most information is based on what is in records)
  5. cases may be more likely to recall past exposures than controls (noncases). May result in recall bias (type of information bias)
38
Q

How do experimental studies measure occurrence?

A

risk
incidence rate
incidence odds

39
Q

How do experimental studies measure association?

A

risk difference/ratio
rate difference/ratio
odds ratio

40
Q

How do cross sectional studies measure occurence?

A

prevalence proportion / odds

41
Q

How do cross sectional studies measure associatoin?

A

prevelance difference / ratio/ odds ratio

42
Q

How do cohort studies measure occurence?

A

risk
incidence rate
incidence odds

same as experimental study

43
Q

How do cohort studies measure association?

A

risk difference / ratio
rate difference / ratio
odds ratio

same as experimental study

44
Q

How do case control studies measure occurence?

A

exposure odds

45
Q

How do case control studies measure association?

A

expoure odds ratio

Epi Exam 2 (5 decks)

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