Case
Task 4: confounding
- Course
- Institution
Problem statement and learning goals Answers to exercises task 4
[Show more]
Seller
Follow
zoeverschueren
Reviews received
Content preview
Problem 4 - confoundingLearning goals:
1) What is confounding? (criteria / types)
The term confounding refers to a situation in which a noncausal association between a given
exposure and outcome is observed as a result of the influence of a third factors (confounder)
Confounding results in distortion of the effect of the exposure on disease due to one or more
extraneous variables.
Confounding is more likely to occur in observational than in experimental studies
In an experimental study, the use of randomization reduces the likelihood that the groups
under comparison differ with regard to both known and unknown confounding factors.
Confounding is based on the counterfactual model. This explanation relies on the notion that the
attribution of causation to a particular exposure is based on the concept that the risk of the outcome
observed among individual exposed would have been different in the same individuals if exposure
had been absent.
The common theme with regard to confounding is that the association between an exposure and
outcome is induced, strengthened, weakened or eliminated by a third variable or group of variables.
CRITERIA OF CONFOUNDING
, Problem 4 - confounding
Unidirectional arrow = causal association
Bidirectional arrow = noncausal association
TYPES OF CONFOUNDING
- Positive confounding / bias = away from the null-value
o E.g.: 2 2.5
o Positive association for both the exposure and outcome
o Negative association for both the exposure and outcome
- Negative confounding / bias = towards the null-value
o E.g.: 2 1.5
o Positive for the outcome and negative for the exposure (or the other way around)
- Switch-over confounding / bias (qualitative) = across the null-value
o E.g. 0.7 1,7
The size of the bias due to confounding depends on the strength of the association between the
confounder and outcome and between the confounder and exposure.
Table 8
2) How can you correct and prevent for confounding?
PREVENT
Design:
- Randomization
- Restriction
- Matching
CORRECT
Assessment of confounding effects is carried out for variables that are known or suspected
confounders. The identification of potential confounders is usually based on prior knowledge. In
addition to the prior knowledge about these associations, it is important to verify whether
confounding is present in the study.
There are several approaches for assessing the presence of confounding, which are related to the
following questions:
- Is the confounding variable related to both the exposure and the outcome in the study?
- Does the exposure-outcome association seen in the crude analysis have the same direction
and similar magnitude as the associations seen within strata of confounding variables?
- Does the exposure-outcome association seen in the crude analysis have the same direction
and similar magnitude as that is seen of controlling (adjusting) for the confounding variables?
Is the confounding variable related to both the exposure and outcome variable
Calculation association between exposure and confounder factor:
- Cohort study in total population
- Case-control study in controls
Calculation association between outcome and confounder:
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller zoeverschueren. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $8.62. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
78121 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now