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Epidemiology > Epidemiology Study Designs > Flashcards

Epidemiology Study Designs Flashcards

1
Q

What are the two principal categories of epidemiological study design?

A

Experimental and Observational

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2
Q

What is randomization?

A

Randomization is an allocation procedure that assigns subjects into one of the exposure groups being compared so that each subject has the same probability of being in one group or another.

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3
Q

What is the advantage of randomization?

A

Randomization is a type of insurance (but not a guarantee) that the variables not measured in the study are evenly distributed among the exposure groups.

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4
Q

What are the primary differences between experimental and observational studies?

A

Experimental: Observational:

Randomization to exposure No randomization
Invest.determines exposure Subject deter. expo.
Clinical Trials (test treatments) Descriptive Study
& Community intervention (nat. history, # of
Trials (test prevention) resources & suggest hyp)
Analytic study (test hyp)
and assess causation

MOST EPI STUDIES ARE OBSERVATIONAL

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5
Q

What is directionality?

A

Directionality:

A design option that answers the question, “Which did you observe first, the exposure or the disease?”; can be forward, backwards, non-directional, or ambi-directional.

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6
Q

What is forward directionality?

A

Forward:

The directionality of a study in which the exposure variable is observed before the health outcome is observed; the study proceeds “forwards” over time; a clinical trial and a cohort study always have forward directionality.

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7
Q

What is backwards directionality?

A

Backwards:

The directionality of a study in which the health outcome is observed before the exposure variable is observed; the study proceeds “backwards” over time; a case-control study always has backwards directionality.

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8
Q

What is non-directional?

A

Non-directional:

A characteristic of a study without directionality; a study in which the exposure variable and the health outcome are observed at essentially the same point of time; a cross-sectional study always is non-directional.

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9
Q

What is ambi-directional?

A

Ambi-directional:

The directionality of a study in which exposure variable information is observed both before and after the health outcome is observed; a characteristic of some hybrid designs.

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10
Q

What is a retrospective study?

A

Retrospective:

A study in which the data are derived from past experience; both the study factor and the health outcome occur before the onset of the study.

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11
Q

What is an example of a retrospective study?

A

Case Control studies are always Retrospective

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12
Q

What are weaknesses of the retrospective study?

A

They are more likely to have information bias due to measurement error in the records or personal recollection of information.

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13
Q

What is a prospective study?

A

Prospective:

A study in which both the study factor and the health outcome occur after the study onset; new data are used.

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14
Q

What is the timing (retrospective or prospective) important to the study design?

A

The timing of the study will affect whether or not the study has measurement error and information bias.

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15
Q

Why is the directionality of the study important?

A

It affects whether or not the study has a selection bias. It also helps the researcher determine the antecedent and the consequent as well as the causation.

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16
Q

What is a clinical trial?

A

A clinical trial is an experimental study that compares health benefits of two or more treatments.

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17
Q

What is the purpose of a clinical trial?

A

To test the efficacy of preventative or therapeutic intervention.

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18
Q

What is the long range goal of a preventative trial?

A

The long range goal of a preventative trial is to prevent disease.

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19
Q

What is the long range goal of a therapeutic trial?

A

The long term goal of a therapeutic trial is to cure or control a disease.

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20
Q

What are examples of preventative trials?

A

Studies of vaccine efficacy, studies of the use of aspirin to prevent coronary disease, studies of exercise and diet modification in disease prevention.

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21
Q

What are examples or therapeutic trials?

A

Therapeutic trials are typically conducted by pharmaceutical companies to test new drugs for treating disease.

22
Q

What are key features of clinical trials?

A

Randomization, Blinding, Ethical concerns, and intention to treat analysis

23
Q

What type of trials are conducted on individuals with a particular disease to assess a possible cure or control for disease?

A

Therapeutic Trials

24
Q

What type of trial would wish to asses to what extent, if any, a new type of chemotherapy prolongs the life of children with acute lymphatic leukemia?

A

Therapeutic Trials

25
Q

What trials can be conducted on either individuals or entire populations?

A

Preventative Studies

26
Q

In what type of trial would the following study fall into? One community is assigned at random to receive sodium fluoride to the water supply while the other continued to receive the water without supplementation to show the reduction of tooth decay?

A

Preventative Studies

27
Q

What are the three categories of observational study designs?

A
  1. Basic Designs: Cohort, Case-Control, and Cross-sectional
  2. Hybrid Designs: Nested Case-Control, Case-Cohort
  3. Incomplete Designs: Ecologic, Proportional
28
Q

What observational study design is the most similar to a clinical trial?

A

The cohort study, in which you follow the same group of individuals with similar attributes to see the development of a health outcome over time.

29
Q

What are advantages of a cohort study?

A
  1. The forward directionality allows the investigator to be reasonably sure that the hypothesized cause preceded the disease/outcome.
  2. In a cohort study, the disease status does not affect how the subjects are selected, so it is free of certain selection bias.
  3. A prospective cohort study design is less prone to obtaining incorrect information that leads to an information bias
  4. A Cohort Study can study several diseases, because several outcomes can be determined from follow up
  5. They are useful for examining rare exposures
  6. Retrospective cohort studies are cost effective and quick, e.g. occupational studies
30
Q

What are the characteristics of a cohort study?

A

Cohort Studies are always a follow up study.

In Cohort Studies, sample populations are grouped according to their exposure prior to the appearance of the health outcome/disease.

This makes the directionality of the study always forward.

Cohort studies can be retrospective or prospective.

31
Q

What are disadvantages of a cohort study?

A
  1. A prospective cohort study is costly and time consuming
  2. Loss of subjects due to: migration, lack of participation, withdrawal, and death which leads to biased results
  3. Statistically and practically inefficient for a rare disease with long latency (need to conduct follow up over long period of time with high number of subjects except in retrospective study)
  4. The exposed are followed up more closely than the unexposed creating a high exposure-disease relationship where none exists.
32
Q

What are characteristics of a case-control study?

A 
It is a basic observational study design
backwards directionality
cheap and quick
very prone to bias compared to a cohort design
Most are retrospective

The study design starts with cases and non cases of a disease and proceeds backwards to determine exposure history.

33
Q

What are advantages of the case-control study?

A

They are cost effective and quicker
They produce sufficient number of cases, especially in rare diseases or diseases with long latency
They can use a smaller sample size
They can evaluate the affect of a variety of exposures

34
Q

What are disadvantages of the case-control study?

A

Do not allow for many diseases to be studied
They do not allow for risk of disease to be estimated directly because they work backwards from health status to find the exposure
They are more susceptible to selection bias since exposure occurred before the cases were selected
More susceptible to information bias because they tend to be retrospective
Not efficient for rare exposures

35
Q

What are two common types of controls?

A

Population-based and hospital-based controls

36
Q

What are characteristics of population based controls?

A

In a population-based case-control study, cases and controls come from the same source.

37
Q

What are characteristics of hospital-based controls?

A

Hospital-based controls are easily accessible, tend to be cooperative, and are inexpensive

Hospital-based controls are not usually representative of the source population and may represent an illness caused by the exposure.

38
Q

What are the characteristics of a cross-sectional study?

A

It assess disease and exposure at a fixed point in time or for a short period of time.

It provides a snapshot of the health experience and patterns of disease occurrence

Always non-directional

Always retrospective

39
Q

What are advantages of the cross-sectional study?

A

It is the most representative of the population being studied
It is the lease expensive and most convenient of all observational studies
It can generate hypotheses of common diseases that have a long duration

40
Q

What are disadvantages of the cross sectional study?

A

It can only recognize existing cases at a point in time (rather than new cases over follow up period)

Cannot establish if the exposure preceded the disease or if the disease influenced the exposure

Includes cases that survive to be available for study (nonsurvivors are excluded)

Short duration disease may be underrepresented

41
Q

What is a case-cohort study?

A

It is a hybrid study design.

It is prospective and had backwards directionality

42
Q

What are advantages of the case-cohort study

A

Controls derive from the source population
several diseases can be studied
more cost and time-efficient than a cohort study
a risk ration can be estimated from case-cohor studies

43
Q

What are disadvantages of the case-cohort study?

A

It is more prone to measurement error than a cohort study

More expensive and time consuming than a case control study

44
Q

What are incomplete study designs?

A

Incomplete designs:

Observational studies in which information is missing on one or more relevant factors,

45
Q

What is an ecologic study?

A

Ecologic study:

An observational study in which the unit of analysis is a group, often defined geographically, such as a census tract, a state, or a country; primary criticism : there is no data on individuals.

46
Q

What is an ecologic fallacy?

A

Conclusions obtained from ecologic studies may not carry over to individuals. i.e. a high incidence in AIDS and TB in some states does not mean that most individuals who have AIDS also have TB

47
Q

What is missing from an ecologic study?

A

The ecologic study has data on the number of exposed persons and the number of cases within each group (state, country, etc) BUT it does not have the number of exposed cases.

48
Q

What is a proportional study?

A

Proportional study:

An observational study that only includes observations on cases without information about the candidate population at risk for developing the health outcome; sometimes referred to as a numerator study.

49
Q

What are the two types of proportional studies?

A

Mortality and Morbidity

50
Q

What information is missing from proportional studies?

A

They do not include informations about the candidate population-at-risk because it only looks at cases. Also traditional measures of effect such as risk ratios and odds ratios cannot be computed

51
Q

What is useful about proportional studies?

A

They can generate hypotheses and conduct preliminary tests of etiologic hypotheses.

Epidemiology (5 decks)

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