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Brush up M&T - Artikel Z - Bias and confouding

14 important questions on Brush up M&T - Artikel Z - Bias and confouding

What are four explanations for an observed association?

1. Random error (chance)
2. Confounding
3. Bias (systematic error)
4. Causality

What are two types of bias?

- selection bias = invalid comparison due to selection of incomparable groups
- information bias = invalid comparison due to incomparable data collection

In which study design can selection bias be found?

1. Case-control = through selection in the study the exposure is more or less present in either the case or control group, compared with the truth
2. Cohort study = in either the exposed or unexposed group the disease (outcome) occurs more or less than truly present
--> most present in case-control studies because controls are selected by the researcher

In which two study designs does information bias occur?

Case-control = data collection differs between cases and controls with regards to the exposure
Cohort study = data collection differs between the exposed and unexposed with regard to the disease/outcome

What is recall bias, and in which study does it occur the most?

Bias due to differences in accuracy of recall between cases and non-cases
Occurs in case-control studies
Solution: objective data collection and comparable data collection

Differential vs. Non differential misclassification

Differential misclassification = information bias
- cohort = misclassification of the outcome depends on the exposure
- case-control = misclassification of the exposure depends on the disease/case status

Non-differential misclassification
- misclassification of outcome (cohort) or exposure (case-control) does not depend on exposure (cohort) or disease (case-control)
- no systematic error, no bias -> dilution of the effect
- occurs in both groups, equal between groups

Selection vs. Information bias

Selection bias
• Invalid comparison through differential selection of groups
• Mainly in case-control studies
• Mainly incorrect selection of the control group

Information bias:
• Invalid comparison through differential data collection
• Recall bias: mainly in case-control studies
• Observer bias: both in case-control as in cohort studies

What is the defenition of confounding?

A third factor explains the association between the exposure and the outcome. The 'effect' of the exposure on the disease is in fact the effect of the confounding fact

What is the difference between confounding and bias?

The observation is valid in contrast to bias (systematic error)
Confounding concerns the causal interpretation of the association

What are the three properties of a confounding factor?

1. Confounding factor is a risk factor of the disease/outcome
2. The confounding factor is associated with the exposure
3. The confounding factor may not be a consequence of the exposure: may not lie in the causal pathway between exposure and outcome

How to prevent confouncint/adjust confounding?

First, you need to identificate the confounding factor(s). This is based on external information --> knowledge, previous research, logic and not on statistical significance!
Then, you prevent/adjust for confounding:

In the design of the study (prevent)

randomisation = all known and unknown factors are equally distributed
restriction = known confounding factors
matching = known confounding factors

In analysis (adjust)

stratification (known)
multivariate regression analysis (known)

What is the disadvantage of matching?

In case control you may introduce bias -> solved with matched analysis

How is stratificatino used in practice?

1. Make 2x2 table
2. Calculate effect for each stratum
3. Pool effects of the strata
4. Compare corrected effect estimate with the crude estimate

Which models can be used for regression analysis (to adjust for confounding)?

- linear regression
- logistic regression
- cox regression

The question on the page originate from the summary of the following study material:

Design and analysis of biomedical studies

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Brush up M&T - Artikel Z - Bias and confouding

14 important questions on Brush up M&T - Artikel Z - Bias and confouding

What are four explanations for an observed association?

What are two types of bias?

In which study design can selection bias be found?

In which two study designs does information bias occur?

What is recall bias, and in which study does it occur the most?

Differential vs. Non differential misclassification

Selection vs. Information bias

What is the defenition of confounding?

What is the difference between confounding and bias?

What are the three properties of a confounding factor?

How to prevent confouncint/adjust confounding?

What is the disadvantage of matching?

How is stratificatino used in practice?

Which models can be used for regression analysis (to adjust for confounding)?

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