Causality, Bias and Confounding

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?

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