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EPIDEMIOLOGY > 7. Case Control, Ecological, and Cross-sectional studies > Flashcards

7. Case Control, Ecological, and Cross-sectional studies Flashcards

1
Q

What is a case control study?

A

With two groups, one group has the disease of interest (cases) and a comparable group is free from the disease (controls)

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2
Q

What do case control studies identify?

A

possible causes of disease by finding out how the groups differ with respect to exposure to some factor

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3
Q

What are 5 characteristics of case-control studies?

A
  1. A single point of observation
  2. Unit of observation and the unit of analysis are the individual
  3. Exposure is determined retrospectively
  4. Does not directly provide incidence data
  5. Data collection typically involves a combination of both primary and secondary sources
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4
Q

What are two tasks involved in case selection?

A
  1. defining a case conceptually

2. identifying a case operationally

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5
Q

Is there a need to be specific in identifying cases?

A

yes

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6
Q

What should the ideal controls have? why?

A

the same characteristics as the cases (except for the exposure of interest)

if equal in all respects then one would be stronger in disease status to the exposure of interest

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7
Q

What are population based controls? And what are some examples of it?

A

obtainign a list that contains names and addresses of most residents in the same geographic area as the cases

examples are driver’s licenses, taxes, voting, telephone directories

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8
Q

What are 3 examples of sources of controls?

A
  1. population based controls
  2. patients from the same hospital
  3. relatives of cases
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9
Q

What does it mean when the odds ration is 1?

A

it means there is no association

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10
Q

When does an Odds Ratio (OR) provide a good approximation of relative risk?

A
  1. when controls are representative of a target population
  2. cases are representative of all cases
  3. the frequency of disease in the population is small
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11
Q

What is the odds ratio statistical significance with 2?

A

suggests cases were twice as likely as controls to be exposed

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12
Q

What is happening when an odds ratio is less than 1?

A

suggests a protective factor

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13
Q

What are the 4 advantages of case-control studies?

A
  1. tend to use smaller sample sizes than surveys or prospective studies
  2. quick and easy to complete
  3. cost effective
  4. useful for studies of rare diseases
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14
Q

What are 4 limitations of case-control studies?

A
  1. unclear temporal relationships between exposures and diseases
  2. use of indirect estimate of risk
  3. representativeness of cases and controls often unknown
  4. recall bias
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15
Q

What is a nested case-control study?

A

a type of case-control study in which cases and controls are drawn from the population in a cohort study

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16
Q

What are 2 advantages of nested case-control studies?

A
  1. provides a degree of control over confounding factors

2. reduces cost because exposure information is collected from a subset of the cohort only

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17
Q

What is recall bias?

A

A systematic difference in the “recall” of exposure based on case/control status

18
Q

Are “cases” more apt to over-report certain suspected risk exposures after disease diagnosis?

A

yes

19
Q

What type of data is more prone to recall bias?

A

self-reported

20
Q

What is an objective source to collect data from?

A

existing medical records

21
Q

Do both case-control studies and retrospective cohort studies relay on assessment of exposure history?

A

yes

22
Q

What is the unit of analysis in an ecological study?

A

the group, not an individual (essentially you can’t create a 2x2 chart)

23
Q

What can ecological studies be used for?

A

for generating hypotheses

makes use of secondary data

advantageous with cost and duration

24
Q

Is the level of exposure for each individual in the unit of an ecological study known or unknown?

A

unknown

25
Q

What is an ecological comparison study?

A

involves an assessment of the correlation between exposure rates and disease rates among different groups over the same time period

26
Q

What is an ecological trend study?

A

involves correlation of changes in exposure with changes in disease within the same community, country, or other aggregate unit

27
Q

When does ecologic fallacy occur?

A

Occurs when incorrect inferences about the individual are made from group level data

28
Q

What is ecologic fallacy?

A

when observations made at the group level don’t represent the exposure-disease relationship at the individual level but that is how it’s expressed

29
Q

What are the implications of the ecologic fallacy?

A

the conclusions obtained from an ecologic study may be the reverse of those from a study that collects data on individual subjects

30
Q

What does individual data do to ecologic data?

A

reverses the conclusion

31
Q

What are 2 advantages of ecological studies?

A
  1. quick, simple, inexpensive

2. good approach for generating hypotheses when a disease is of unknown etiology

32
Q

What are 2 disadvantages of ecological studies?

A
  1. ecological fallacy

2. imprecise measurement of exposure and disease

33
Q

What kind of study is also termed prevalence study?

A

A cross-sectional study

34
Q

What kind of study is this?

When exposure and disease measures are obtained a the individual level.

A

A cross-sectional study

35
Q

How many periods of observation are there in cross-sectional studies?

A

there is a single period of observation

36
Q

Are exposure and disease histories collected simultaneously in cross-sectional studies?

A

yes

37
Q

In which study is both probability and non-probability sampling used?

A

cross-sectional studies

38
Q

What are 5 uses of cross-sectional studies?

A
  1. Hypothesis generation
  2. intervention planning
  3. planning health services and administering medical care facilities
  4. estimation of the magnitude and distribution of a health problem
  5. examines trends in disease or risk factors that can vary over time
39
Q

What are 4 limitations of cross-sectional studies?

A
  1. limited usefulness for inferring disease etiology (association but not a causal inference)
  2. do not provide incidence data
  3. cannot study low prevalence diseases
  4. cannot determine temporality of exposure and disease
40
Q

How should you interpret an odds ratio in a cross-sectional study?

A

2 suggests the exposes were twice as likely to have disease than unexposed

EPIDEMIOLOGY (8 decks)

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