Lecture 8: Casuality, bias and confounding Flashcards
What is a casual inference?
determining the effect of a phenomenon part of a wider system
What is the name given to what would have happened in a study if we’d done things differently?
counterfactual
What is another name for an estimate of a counterfactual?
Control
What term is used to describe groups of people in a study who are comparable on average?
exchangeable
What is the easiest way to ensure exchangeable study groups?
randomisation
What is random sampling error?
-The random error in our population estimate(s) that results from chance fluctuations in the profile of our sample
Is error caused by random or non-random factors?
non-random
What is bias?
a non-random, systematic error
What is precision?
a measure of how close a series of measurements are to one another
What is accuracy?
how close a measurement is to the true value
What is confounding bias?
Distortion of the causal association between two variables, due to a common shared cause (a confounder)
What is a confounder?
a third variable that influences an association without being measured
What is conditioning?
the process of reducing confounders by examining like-for-like participants (grouping participants into exposed and non-exposed groups)
Give 3 forms of conditioning confounders:
1) restriction
2) stratification
3) covariate adjustment
Describe restriction as a form of conditioning:
restricting the sample to a single value of the confounder
Describe stratification as a form of conditioning:
calculating category-specific effects for different levels of the confounder
Describe covariate adjustment as a form of conditioning:
adjusting the cofounders in a regression of the association
What causes selection bias?
a systematic difference between those selected into a study sample and those that were not selected
Give 3 types of selection bias:
1) sampling bias
2) participation bias
3) attrition bias
What is sampling bias?
a failure to sample evenly across the population (not generalisable)
What is participation bias?
people having different preferences or opportunities to participate in research
What is attrition bias?
a loss of participants from the study which may be unbalanced by the exposure
What causes information bias?
a systematic error in reporting, measurement or the recording of error
Give 3 types of information bias:
1) response bias
2) recall bias
3) measurement bias
What is response bias?
people responding in inaccurate or untruthful ways by wanting to give the right answer or downplaying undesirable traits
What is recall bias?
people having different abilities to remember past information
What is measurement bias?
a measurement that under or over reports systematically
What causes experimenter bias?
the behaviours and actions of the experimenter whether conscious or unconscious
Give two types of experimenter bias:
1) confirmation bias
2) results bias
What is confirmation bias?
where findings we expect are more likely to be accepted and those that aren’t are refuted
What is results bias?
being more likely to chase positive associations, seek novel results or publish positive results
