Bias and confounding

1. Bias and confounder
Presented by : Erum Ali Akbar

2. What is bias?
Bias is any systematic error in an epidemiologic
study that results in an incorrect estimate of the
association between exposure and the health
outcome. … The consequence of bias is systematic
error in the risk ratio, rate ratio, or odds ratio estimate.

3. Types of Error :

4. Source of resources in epidemiology :

5. Types of bias :
 There are two types of bias:
1: Selection bias
2: Information bias

6. What is selection bias?
When a systematic error is made inselecting one
or more of the study group that will be compared
.

7. Example of selection bias:
In a Control study of smoking and
Chronic lung disease, the association of
Exposure with disease will tend to be weaker
If controls are selected from a hospital
Population (because smoking causes many
Diseases resulting in hospitalization) than if
Controls are selected from the community.

8. Information bias :
information gathered regarding
exposure and/ or disease outcome is incorrect.

9. Example of information bias:
Missing data can be a major cause of
information bias, where certain groups of
people are more likely to have missing data.
An example where differential recording may
occur is in smoking data within medical
records. … The bias was more likely when the
exposure is dichotomized.

10. What is confounding?
Confounding is one type of systematic error
that can occur in epidemiologic studies. …
Confounding is the distortion of the
association between an exposure and health
outcome by an extraneous, third variable
called a confounder