Epidemiology 4 Flashcards
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Case-control pairs that had the same exposure are termed ______________________.

concordant

Case-control pairs with different exposure experience are termed ____________________________________.

discordant pairs

Regarding the 2 x 2 table for matched pairs for case-control studies, explain the a and b pairs.

a pairs are pairs in which both the case and the control were exposed; b pairs are pairs in which the case was exposed and the control was not.

Calculation of the odds ratio in such a matched pair study is based on the _____________________ pairs, and these are the _____ and ________ pairs.

<p>discordant, b, c</p> Signup and view all the answers

Matched pairs odds ratio equals ________________________.

<p>b pairs over c pairs</p> Signup and view all the answers

The odds ratio matched pairs formula consists of:

<p>number of exposed controls paired with exposed cases over number of exposed controls paired with not exposed cases.</p> Signup and view all the answers

In the matched pairs 2 x 2 table: a pairs are in the ______________; b pairs are in the ________________; c pairs are in the __________________; and d pairs are in the _____________________.

<p>top left box, top right box, bottom left box, bottom right box</p> Signup and view all the answers

Cross sectional studies are studies in which ____________________ and ____________________ are collected ____________________________.

<p>exposure, outcome, at the same time</p> Signup and view all the answers

With cross sectional studies, it is as if we are viewing ____________________________________________.

<p>a snapshot of the population at a certain point in time</p> Signup and view all the answers

What is an important consideration to include in case control studies?

<p>Whether to include incident cases of disease or prevalent cases of disease.</p> Signup and view all the answers

What is a problem with the use of incident cases in case control studies?

<p>We must often wait for new cases to be diagnosed.</p> Signup and view all the answers

Which type of case obtains better results?

<p>Incident cases.</p> Signup and view all the answers

Why does one type of case obtain better results?

<p>Incident cases obtain better results because identified risk factors may be related more to survival rather than disease development.</p> Signup and view all the answers

Which cases are more likely to obtain longer-term survivors? Why?

<p>Prevalent cases, because they include longer-term survivors.</p> Signup and view all the answers

What is the formula for prevalence cases?

<p>Number of exposed cases over total number of cases.</p> Signup and view all the answers

What is the formula for prevalence of controls?

<p>Number of exposed controls over total number of controls.</p> Signup and view all the answers

Are there biases that are possible with case control studies?

<p>True</p> Signup and view all the answers

What is recall bias?

<p>Differential recall about exposure between cases and controls.</p> Signup and view all the answers

Is recall bias more or less serious than other types of bias?

<p>False</p> Signup and view all the answers

Recall bias has to do with ___________________________________. Give an example.

<p>Differential recall. For example, people with a disease may remember an exposure, whereas people without a disease may not.</p> Signup and view all the answers

The quality of the data in case control studies is to some extent determined by _________________________________.

<p>The patient's ability to accurately recall past exposure.</p> Signup and view all the answers

Recall bias may occur when ______________________________?

<p>The information provided on exposure differs between cases and controls.</p> Signup and view all the answers

Recall bias may result in either __________________________ or __________________________________ of the association between exposure and outcome.

<p>An underestimation or overestimation.</p> Signup and view all the answers

Give examples of when selection bias can occur.

<p>When there is a difference between those who participate in a study and those who do not.</p> Signup and view all the answers

What problems must be kept in mind to avoid selection bias? What are they?

<p>Selecting from a single hospital, which may not be representative.</p> Signup and view all the answers

Give another example of a problem to avoid concerning selection bias.

<p>Choosing a hospital that treats severely ill patients.</p> Signup and view all the answers

Is it difficult to select appropriate controls in epidemiology?

<p>True</p> Signup and view all the answers

The way the controls are selected is a major determinant in whether ___________________________________.

<p>One can conclude if there is an association between an exposure and the disease in question.</p> Signup and view all the answers

What is another type of bias in case control studies?

<p>Observation bias.</p> Signup and view all the answers

Why can observation bias occur?

<p>Due to the investigator's prior knowledge, affecting measurement or interpretation.</p> Signup and view all the answers

What is observation bias?

<p>Knowledge of disease status influences reporting by subjects or interpretation by the investigator.</p> Signup and view all the answers

Give an example of observation bias.

<p>Reading and measuring blood pressure may be biased.</p> Signup and view all the answers

What does misclassification bias have to do with?

<p>Errors in the categorization of exposure or disease.</p> Signup and view all the answers

How many forms of misclassification bias are there and what are they?

<p>Two forms: differential and nondifferential misclassification.</p> Signup and view all the answers

Explain how case control and exposure data can be misclassified.

<p>Cases can be misclassified as controls and vice versa, or misclassified in their exposure data.</p> Signup and view all the answers

Explain about differential misclassification. Give an example.

<p>The rate of misclassification differs in study groups. For example, unexposed cases might be misclassified as exposed more often.</p> Signup and view all the answers

What does nondifferential misclassification result from, and what is the inherent problem?

<p>Inaccuracy in information collection across study groups.</p> Signup and view all the answers

What is the usual effect of nondifferential misclassification?

<p>The relative risk or odds ratio is diluted and shifts toward 1.0.</p> Signup and view all the answers

Nondifferential misclassification happens when ______________________________________________.

<p>The information is incorrect but the same across groups.</p> Signup and view all the answers

In case control studies, nondifferential misclassification can happen when _____________________________________.

<p>Exposure status is incorrect for both cases and controls.</p> Signup and view all the answers

What is differential misclassification?

<p>It relates to exposure or disease nonrandomly, potentially exaggerating or underestimating an effect.</p> Signup and view all the answers

Which is more serious: differential misclassification or nondifferential misclassification?

<p>False</p> Signup and view all the answers

Nondifferential misclassification happens to exposure or disease in the same or different proportions?

<p>False</p> Signup and view all the answers

Is nondifferential misclassification random or non-random?

<p>False</p> Signup and view all the answers

Nondifferential misclassification ________________________________ true relation of risk, and it is biased towards ____________________________.

<p>Underestimates, the null.</p> Signup and view all the answers

Information bias can occur when _______________________________ about the subjects in the study ____________________________________.

<p>Means for obtaining information are inadequate.</p> Signup and view all the answers

What results when information about the subjects is inadequate?

<p>Some of the information gathered regarding exposures and/or disease outcomes is incorrect.</p> Signup and view all the answers

What are the strengths of case control studies?

<p>They are quick and inexpensive, well-suited for long latency diseases, optimal for studying rare diseases, and examine multiple factors.</p> Signup and view all the answers

What are the weaknesses of case control studies?

<p>Not good for rare exposures, compute incidence rates, difficult to establish temporal relationships, and prone to biases.</p> Signup and view all the answers

What is the measure of association used in case control studies called?

<p>Odds ratios.</p> Signup and view all the answers

Regarding measures of association used in case control studies, what is this used in place of? Why?

<p>Relative risk, because it cannot be calculated directly in case control studies.</p> Signup and view all the answers

What can be used instead of relative risk?

<p>Odds ratio.</p> Signup and view all the answers

In a case control study, do we know the incidence in the exposed or the non-exposed population? Why?

<p>No, because we start with diseased people and non-diseased people.</p> Signup and view all the answers

Does the odds ratio allow us to obtain a good estimate of the relative risk?

<p>True</p> Signup and view all the answers

How can the odds of an event in epidemiology be defined?

<p>The ratio of the number of ways the event can occur to the number of ways the event cannot occur.</p> Signup and view all the answers

Is there a difference between probability and odds?

<p>True</p> Signup and view all the answers

Can we calculate the relative risk directly to determine if there is an association between exposure and disease? Why?

<p>False</p> Signup and view all the answers

By using the odds ratios, what questions do we ask?

<p>What are the odds that a case was exposed? What are the odds that a control was exposed?</p> Signup and view all the answers

How can we calculate the odds ratio?

<p>By calculating the ratio of the odds that the cases were exposed to the odds that the controls were exposed.</p> Signup and view all the answers

Give the formula for the odds ratio.

<p>(a/c) over (b/d) equals ad over bc</p> Signup and view all the answers

The odds ratio can be interpreted the same way as ______________________________.

<p>Relative risk.</p> Signup and view all the answers

If the exposure is not related to the disease, the odds ratio will equal _______.

<ol> <li></li> </ol> Signup and view all the answers

If the exposure is positively related to the disease, the odds ratio will be ______________________________.

<p>Greater than 1.</p> Signup and view all the answers

If the exposure is negatively related to the disease, the odds ratio will be _________________________.

<p>Less than 1.</p> Signup and view all the answers

The odds of case exposure is written as _________________________.

<p>The probability a case was exposed over the probability a case was not exposed.</p> Signup and view all the answers

How do you write the odds of control exposure?

<p>Written the same as the case, substituting control for case.</p> Signup and view all the answers

What is the formula for odds ratio in general?

<p>Number of cases exposed multiplied by number of controls not exposed over number of cases not exposed multiplied by number of controls exposed.</p> Signup and view all the answers

If odds ratio = 1, then exposure is ______________________.

<p>Not related.</p> Signup and view all the answers

If odds ratio > 1, then exposure is ______________________.

<p>Related.</p> Signup and view all the answers

If odds ratio < 1, then exposure is _______________________ .

<p>Negatively related.</p> Signup and view all the answers

In a case control study, only the odds ratio can be calculated as _____________________________________________.

<p>A measure of association.</p> Signup and view all the answers

The odds ratio is a good approximation of the relative risk in the population when:

<ol> <li>the cases studied are representative of all the people with the disease in the population from which cases were drawn; 2. When the controls are also representative; 3. When the disease being studied does not occur frequently; 4. When disease occurrence is infrequent.</li> </ol> Signup and view all the answers

In selecting the study population in case control studies, controls are often selected by ______________________________.

<p>Matching each one to a case according to related variables.</p> Signup and view all the answers

In case control studies, the results are then analyzed in terms of ______________________________________.

<p>Case-control pairs rather than for individual subjects.</p> Signup and view all the answers

Considering this, if a person is either exposed or not exposed, then there are only ____________ types of case-control pairs that are possible regarding case-control combinations in regards to exposure history.

<p>Four.</p> Signup and view all the answers

The ___________ types of case-control pairs include __________ types that are listed as ____________________________ pairs, and ___________ types that are listed as _____________________ pairs.

<p>Four, two types listed as concordant pairs, two types listed as discordant pairs.</p> Signup and view all the answers

The two types of concordant pairs include the following:

<ol> <li>Pairs in which both the case and the control were exposed; 2. Pairs in which neither the case nor the control were exposed.</li> </ol> Signup and view all the answers

The two types of discordant pairs include the following:

<ol start="3"> <li>Pairs in which the case was exposed and the control was not; 4. Pairs in which the control was exposed and the case was not.</li> </ol> Signup and view all the answers

Study Notes

Case Control Studies

  • Important to decide between using incident (new) cases or prevalent (existing) cases.
  • Incident cases yield better results despite practical challenges; they reduce potential confounding from survival bias.
  • Prevalent cases may skew results by including long-term survivors who may not represent all patients.

Bias in Case Control Studies

  • Multiple biases exist:
    • Recall Bias: Involves differential recall of exposure between cases and controls; can suggest false relationships.
    • Selection Bias: Occurs when study groups differ; impacts generalizability, especially if cases are drawn from a single source.
    • Observation Bias: Results from investigator's knowledge influencing data collection and interpretation.
    • Misclassification Bias: Errors in categorization of exposure or disease status; can be differential or nondifferential.

Recall Bias

  • More severe than other biases; arises from varying ability to recall past exposures.
  • May lead to under or overestimation of associations between exposure and outcomes.

Selection Bias

  • Selection methods must ensure controls are representative; using a single institution may limit generalizability.
  • Unique characteristics of patients with severe conditions may not reflect the broader population.

Misclassification Bias

  • Two forms exist:
    • Differential: Misclassification varies between study groups.
    • Nondifferential: Inaccuracy is consistent across groups, typically diluting the observed association.

Odds Ratios

  • Measure of association in case control studies, used instead of relative risk since the latter cannot be calculated directly.
  • Defined as the ratio of the odds of exposure in cases to the odds of exposure in controls.
  • Interpreted similarly to relative risk:
    • Odds Ratio = 1 implies no relationship.
    • Odds Ratio > 1 indicates a positive relationship.
    • Odds Ratio < 1 signifies a negative relationship.

Strengths and Weaknesses of Case Control Studies

  • Strengths:
    • Cost-effective and fast to conduct.
    • Suitable for rare diseases and long latency periods.
    • Can assess multiple risk factors for diseases.
  • Weaknesses:
    • Ineffective for rare exposures; challenging to establish temporal relationships.
    • Prone to selection and recall biases.

Matched Pairs in Case Control Studies

  • Controls are often matched to cases based on known risk factors.
  • Analyzed in terms of case-control pairs, focusing on concordant (same exposure) and discordant (different exposure) pairs.
  • Calculation of odds ratios primarily relies on discordant pairs.

Formulae in Case Control Studies

  • Prevalence Formula: Number of exposed cases / Total number of cases.
  • Odds Ratio: calculated as (a/c) / (b/d) or ad / bc.
  • Matched Pairs Odds Ratio: Calculated using discordant pairs (b and c).

Research Considerations

  • Careful selection of appropriate controls is critical to enforcing reliability in study results.
  • Data quality relies heavily on accurate recall from the patients involved.
  • Results analyzed with attention to pairs, enhancing the interpretation of exposure effects.### Matched Pairs 2 x 2 Table
  • In a matched pairs 2 x 2 table, specific pairs of data are categorized into four distinct quadrants.
  • The quadrants are identified as:
    • Top left box contains 'a' pairs.
    • Top right box contains 'b' pairs.
    • Bottom left box contains 'c' pairs.
    • Bottom right box contains 'd' pairs.

Cross Sectional Studies

  • Cross sectional studies involve collecting exposure and outcome data simultaneously.
  • They provide a snapshot or representation of a specific moment in time.
  • These studies allow researchers to examine relationships between variables at one point, but do not establish causation.

Snapshot Perspective

  • Cross sectional studies can be viewed as capturing a snapshot of the entire population at a particular moment, highlighting the status of various variables concurrently.

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Description

This quiz focuses on essential concepts in epidemiology, specifically related to case control studies. It covers critical considerations such as the inclusion of incident versus prevalent cases in study designs. Test your knowledge of these important epidemiological principles.

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