Bias, Confounding and Interaction Flashcards
What are some examples of random error?
Biological variation and sampling errors
- they are usually evenly distributed above and below the true value
What are systematic errors also known as?
Also known as bias (any deviation that is not due to chance alone)
What is the definition of precision?
Precision refers to how well repeated observations agree with each other
What is the definition of accuracy?
Accuracy refers to how well the observed value agrees with the true value
What are some examples of systematic error?
Selection bias, Information bias, Confounding bias
What are the two different types of information bias
Recall bias and Observer bias
What is the definition of bias?
a systematic deviation of results or interferences from the truth or any processes that lead to systematic deviation
What is the definition of selection bias?
systematic difference in the enrolment of participants in a study
that leads to an incorrect result (e.g., risk ratio or odds ratio) or inference.
What is the definition of information bias?
systematic difference in the collection of data regarding the participants in a study
e.g
* incomplete/missed medical records
* incomplete questionnaires
What is the definition of error?
The difference between the true value and the observed/ estimated one
What is the definition of random error?
Unknown and unnpredictable changes in the experiment of observation
What are some major sources of random error?
- Biological variation
- sampling errors
- measurement errors
these are all evenly distributed above and below the true value
Where do systematic errors have a tendency to be?
Either above or below the true value
What is the net random error over a large number of observations?
around zero, estimate may be imprecise but not inaccurate
What are measurement errors referred as?
misclassification
What is the definition of information bias/ misclassification?
- Incomplete medical records
- Patients completing questionnaires incorrectly
- misinterpretation of records
What are the two different types of information bias?
- Recall bias- differential recall of information by cases and controls
- Observer bias- bias in information collected by the investigator
What is an example of observer bias?
Those affected by a disease may make more of an effort to remember details
What is an example of recall bias?
More likely to remember the overly heavy/ light foetuses that were aborted
What is the definition of confounding?
The distortion of the association between an exposure and a health outcome by a third variable that is associated to both
What must a variable be to be a ‘counfounder’?
- The factor must be independently associated with the disease
- The factor must also be associated with the exposure being investigated
- It should not lie on the causal pathway between exposure and disease
What is the effect of confounding?
- Confounding factors can lead to bias in the estimate of the impact of the exposure being studied
What are four ways you can deal with confounding?
In the design stage preferably
- Restriction- only select units in relation to the cofounder
- Randomisation- clinical trials so there is a similiar distribution of the cofounder in both groups
- pair matching- selecting for each case, one or more controls with similiar characteristics
- frequency matching- ensuring that as a group the cases have similiar characteristics to the controls
How can you deal with confounding at the analytical stage?
- Stratification- estimate measures of association within different levels of the confounding factor
- Statistical modelling- multivariate analyses can control for confounding
What is the definition of the odds ratio?
The odds ratio represents the odds that an outcome will occur in a particular exposure, compared to the odds of the outcome occuring in the absence of that exposure
What does an odds ratio of 1 >1 and 1< mean
1= esxposure does not effect the odds
>1 = exposure associated with higher odds
<1= exposure associated with lower odds
How would you know that something is a confounding variable in terms of odds ratio?
If you take it out as a variable and there is a difference in the odds between that and the crude odds ratio
How will you know if there is effect modification based on the stratum-specific odds ratio?
The startum-species estimates will differ from eachother entirely
Summarise confounding
Remove or account for the effect of the confounder in order to get nearer to the truth (actual measurement of effect).
Effect of the exposure is the same for all categories of the confounding factor
Summarise interaction
Interaction is an important property of the association between two factors (detect and describe)
The factor modifies the effect of other: effect varies across category of the other factor
