Cohort and Case Control Studies- Krysiak

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25 Terms

1
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Analytical Observational Studies evaluates the relationship between 2 or more variables and do or do not involve control groups?

do

2
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Can observational studies claim cause and effect?

no!

  • we are only aiming at quantifying an association between variables

  • aka in analytical observational studies evaluating the “relationship” NOT CLAIMING CAUSE OR EFFECT bc this is OBSERVATIONAL

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What questions can we answer with observational studies?

  • measure effect of exposures

    • ex: tobacco smoke, unhealthy diet, illicit drug use, etc.

  • we can add to our understanding of

    • adverse effects of meds, special populations (kids, pregnant, elderly), co-existing disease states, off-label uses

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Do observational studies measure “the usual conditions” or “artificial conditions”? What are those conditions?

the usual conditions:

  • a typical clinical setting

  • interventions NOT ASSIGNED

  • measures real world effects

(FYI: artificial conditions would be like in a lab, under watch and care)

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What are incidence rates?

number of people w/ NEW diagnosis of disease/ number of ppl at risk

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What are prevalence rates?

number of people with new AND existing disease/ number of ppl at risk

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What are point prevalence rates?

number of people w/ new and existing disease/ number of people at risk AT A SPECIFIC POINT IN TIME

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Review:

What are the main differences between the 3 types of rates?

incidence- think NEW people diagnosed

prevalence- NEW people+ Previously diagnosed people

point prevalence- like prevalence, EXCEPT it’s a specific point in time

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Purpose of cohort study:

  • presence/absence of the suspected causative factor “risk factor

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Purpose of case-control study:

  • presence/absence of the suspected outcome “problem”

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Is a cohort study prospective, retrospective, or both?

BOTH

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Advantages and disadvantages of prospective cohort studies:

  • advantages:

    • gather new data to answer research question

    • use reliable and validated techniques of measurement

    • clarify if the exposure occurred prior to outcome

  • disadvantages:

    • expensive

    • time consuming

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Advantages and disadvantages of retrospective cohort studies:

  • advantages:

    • quickly find results

  • disadvantages:

    • limited to studying things only available in the data

    • errors and omissions of factors

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Is a case-control study prospective, retrospective, or both?

RETROSPECTIVE ONLY

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Example of Cohort study:

FYI

  • basically were comparing a group exposed to a risk factor (smoking) to those not

  • we follow them overtime, and see if the outcome we believe develops (ex: lung cancer)

<ul><li><p>basically were comparing a group exposed to a risk factor (smoking) to those not</p></li><li><p>we follow them overtime, and see if the outcome we believe develops (ex: lung cancer)</p></li></ul>
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Example of case-control study:

FYI

  • we take a group that has an outcome (diabetics) to those who don’t (non-diabetics)

  • we retrospectively look at their histories and draw conclusions from those risk factors

    • ex: we look at all the diabetics history and see they ate candy for every meal versus the control group who ate a balanced diet all their life… we could conclude that maybe the risk factor of eating candy for every meal leads to diabetes…

      • remember CANNOT SAY IT CAUSED THE DIABETES THO

<ul><li><p>we take a group that has an outcome (diabetics) to those who don’t (non-diabetics)</p></li><li><p>we retrospectively look at their histories and draw conclusions from those risk factors</p><ul><li><p>ex: we look at all the diabetics history and see they ate candy for every meal versus the control group who ate a balanced diet all their life… we could conclude that maybe the risk factor of eating candy for every meal leads to diabetes…</p><ul><li><p>remember CANNOT SAY IT CAUSED THE DIABETES THO </p></li></ul></li></ul></li></ul>
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Relative risk is used for __________ studies. Odds Ratio is used for ______________ studies.

relative risk: cohort studies

odds ratio: case-control studies

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How do you calculate relative risk?

  • risk exposed / risk unexposed

    • RR= [a/(a+b)] / [c/(c+d)]

      • WILL GIVE U EQUATION

      • YOU JUST HAVE TO KNOW WHERE ON THE TABLE TO FILL IN

  • RR> 1 means exposure increases risk of outcome

  • RR< 1 means exposure decreases risk of outcome

<ul><li><p>risk exposed / risk unexposed</p><ul><li><p>RR= [a/(a+b)] / [c/(c+d)] </p><ul><li><p>WILL GIVE U EQUATION </p></li><li><p>YOU JUST HAVE TO KNOW WHERE ON THE TABLE TO FILL IN</p></li></ul></li></ul></li><li><p>RR&gt; 1 means exposure increases risk of outcome</p></li><li><p>RR&lt; 1 means exposure decreases risk of outcome</p></li></ul>
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How do you calculate odds ratio?

  • odds of exposure among cases compared to odds of exposure among controls

  • Odds ratio= (a/c)/ (b/d) OR (AD)/(BC)

    • WILL GIVE EQUATION

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Advantages of cohort and case-control studies in general:

knowt flashcard image
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What is the difference between a population- based and nested case-control study?

  • population-based: conducted within a defined base pop

  • nested: conducted within a cohort study

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What are the 3 types of bias?

  1. confounding

  2. selection

  3. recall

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Explain the 3 types of bias:

  • confounding

    • variable other than exposure of interest that affects the outcome

  • selection

    • difference between treatment and control groups resulting from the way they were selected

  • recall bias

    • ppl may remember things differently than how they occurred

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Data sources can be either primary or secondary. Explain each:

Primary: newly gathered for research

  • like questionnaire, interview, etc.

Secondary: collected for another purpose

  • like medical claims databases, electronic medical records

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Helpful table I made for review of cohort/case-control studies:

Cohort

Case-control

presence/ absence of:

risk factor

outcome

type of perspective

both- pro and retro

only RETRO

good for studying rare:

exposures

outcomes

calculating

relative risk

odds ratio

do we have controls?

yes

yes