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epidemiology > case-control study > Flashcards

case-control study Flashcards

1
Q

How is the study designed?

A
  1. Population from which cases and controls are identified
  2. Investigators identify cases of disease and select controls who represent a sample of the source population that produces the cases
  3. Time
  4. Compare exposure in cases and controls.
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2
Q

What study can be used to solve cohort study limitations?

A

case-control study

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3
Q

What is a case-control study

A
  • identifies individuals with a disease (cases) and compares them to individuals without the disease (controls)
  • Past exposures are examined in both groups to assess associations with the disease
  • The study begins by knowing the disease status of participants.
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4
Q

When is it desirable to conduct a case-control?

A
  • When exposure data are expensive or difficult to obtain
  • When diseases have long latent periods, results may take decades to emerge
  • When the disease is rare, a cohort study would require a sample size that is too large.
  • When the population is challenging to follow, a high loss of follow-up may result in biased results.
  • When little is known about the disease, it can evaluate many exposures (and because investigators evaluate more than one hypothesis)
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5
Q

what should you consider when defining a source population?

A

Consider hypothesis, person, place, and time when defining the source population.

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6
Q

What is essential for identifying cases in an epidemiological study?What should the criteria for case definition ensure?

A
  • A clear case definition.
  • it should lead to accurate classification of the disease
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7
Q

What type of sources should be used? From where can cases be identified in a study?

A
  • efficient and accurate
  • Cases presenting to a hospital or clinic
  • Population registries(state cancer registries, notifiable infectious diseases registries)
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8
Q

What is a key similarity between cases in a case-control study and a cohort study?

A

Cases are the same as those that would be included in a cohort study

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9
Q

Why is it important to enroll as many cases as possible? Do case-control studies need to include all cases of disease within a population?

A
  • Cases are statistically precious- enroll as many of them as possible
  • No, they do not need to include all cases of disease occurring within a defined population.
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10
Q

What is the benefit of having restrictive case definitions? How does a restrictive case definition affect sample size?

A

-restrictive cases reduce the number eligible for inclusion, leading to fewer classification errors
- it results in a smaller sample size.

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11
Q

What are controls? other names? The primary purpose of control?

A
  • A sample of the source population that produced cases (referent group or study base)
    -To estimate the exposure distribution in the source population that produced the cases.
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12
Q

Why is it important to know the exposure prevalence among cases and controls?

A

: It allows researchers to measure the association between exposure and outcome.

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13
Q

What is the “would criterion” in control selection?

A

If a control were to develop the disease under study, they should be eligible to become a case in the study.

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14
Q

What are the two necessary requirements for control selection in a case-control study?

A
  • controls must come from the same source population as the cases and random selection is necessary for representativeness
  • controls must be selected independently from the exposure - meaning that their exposure status does not influence their selection
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15
Q

How should controls be selected regarding their exposure status

A

Controls must be selected independently of their exposure to avoid bias.

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16
Q

Where are the three places to find control?

A

nested control
population-based control
hospital or clinic-based controls

17
Q

What are nested controls? Where do they form from?

A
  • These are controls selected from an existing cohort population. Controls represent a sub-set of the full source population
  • form a cohort population/study
18
Q

What are the benefits and disadvantages of nested controls?

A
  • Good news: controls come from a clearly defined source population; already enrolled -> willing participants
  • Bad news: restricted to members of existing cohort; may limit hypothesis that can be studied
19
Q

What is population-based controls? Source?

A
  • These are controls selected from the general population, most suitable when cases are from well-defined geographic area
  • random digit dialing, cell phone or internet subscribers, residence lists, tax lists
20
Q

what are the benefits and disadvantages of population-based controls?

A
  • The good news is that controls often come from well-defined source populations
    = Controls are selected in a way where you know they come from teh same base population as cases do
  • Bad news: very time-consuming, hard to inspire participation, many may not recall past exposure as well as cases
21
Q

What are hospital or clinic-based controls?
what kind of people are chosen?

A
  • Controls selected from among patients at a hospital or clinic
  • Choose control patients with diseases (more often than one) other than the cases of disease
  • Typically used when cases are identified from hospitals
22
Q

what is the benfits and disavatnge of using hospital based controls?

A
  • good news: easy to identify and access - less time and money, the accuracy of exposure recall comparable to cases, more willing participants
  • Bad news: these controls are not randomly selected. This means that hospital-based controls must be carefully selected to accurately represent the exposure history in the source population
23
Q

Which illness makes good hospital controls?

A
  • llness that has the same catchment areas as the cases- This is what we mean when we say controls should come from the same source population as cases
  • Illness that has no relation to risk factors under study - This is what we mean when we say the selection of controls should be independent of exposure
24
Q

What is the purpose of sampling controls?

A
  • This is to determine the exposure distribution in the source population that produced the cases
  • Power calculation helps determine the number of controls needed because we want to be able to detect the difference in exposure levels between cases and controls
25
Q

What can you not calculate? why?

A
  • measures of frequency: risks and rates
  • No longer have the entire denominator of the population at risk (because controls represent a SAMPLE of the total population)
  • Can only calculate using the ODDS RATIO ( relative measure of association )
25
Q

what can you not use when measuring association?

A
  • the margin totals on the right side but can use the bottom totals
  • No absolute measures of association can be calculated (no marginal totals)
26
Q

odd ratio formula? what studies do you use it in?

A

ad/bc
- You would calculate the exposure odds
- In cohort studies, you calculate the disease odds ratio

27
Q

How do you interpret the odds ratio?

A

The odds of developing (health outcomes of interest) among the exposed group is 0.X or XX.XX% times the odds of developing the health outcome of interest among the unexposed group during the time

28
Q

What is the highest ratio for the number of controls to a case?

A
  • When the number of cases is limited, and controls are a lot you can increase the power of the study to detect an association by increasing the size of the control group
  • Up to 4:1 ratios going more than are expensive unless it is premade data
29
Q

Relative measures of association for Odds ration = ?

A

No association between exposure and disease the odds ration =1
If exposure is assoiated with increase ODDS of disease >1
If the exposure is assoiated with decreased odds of diseas <1

30
Q

what formual can odds ration = to?

A

APe - e we do not have the ability to use the marginal totals for a follow-up study
design.
- APt - we do not have the ability to use the marginal totals for a follow-up study design. Also, the RR (risk ratio/rate ratio) and PR (prevalence ratio) cannot be calculated in a case- control study; therefore, the OR must be used

31
Q

what are the methods for samping controls (3)?

A
  • Select from non-cases or survivors at the end of the case diagnosis - survivor sampling
  • Case-base or case-cohort sampling - select from the population at risk at the beginning
  • Risk set-sampling - controls are selected from the population at risk as cases are diagnosed
32
Q

limitations of case control studies?

A
  • often studying single outcome
  • Inefficient for rare exposures
  • More opportunity for systematic bias (recall and selection bias)
  • May be unsure about temporal sequence between exposure and disease
  • Cannot calculate absolute measure of association
33
Q

strengtsh of case-control study?

A
  • Fewer ethical concerns than experimental studies
  • More effiecnet than cohort studies
  • Requires less time and money
  • Fewer subjects needed to measure an association, this is especially helpful when exposure informaion is expensive to obtain
  • No need to wait for long latency diseases to devlop
  • Easy to explore effect of many exposures on an outcome
  • Useful for diseases with little information/unexpokired etiologies
  • Important fr infections disease outbreaks
34
Q

case-crossover study?

A
  • a variant, used to study the effect of transient exposures on teh risk of acute events, cases serve as their own controls, and the exposure frequency during a hazard period is compaed to that from a control period
  • Risk od motor vechile cokkiding while using phone
  • Hazard period: the period of increased risk following the exposure - The exposure frequency during the hazard peirod is compared to a control period
  • Cases serve as their own controls

epidemiology (18 decks)

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