5) Bias And Confounding Flashcards Preview

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Flashcards in 5) Bias And Confounding Deck (14)
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1
Q

Sources of selection bias

A
  • inapporpriate selection of subjects from the study population
  • non random allocation of exposure
  • failure to include subjects in analysis
2
Q

RCT

A
  • randomly allocate exposure and conceal allocation
  • minimise loss to follow up
  • analyse by intention to treat in order to pressure the two groups exactly how they were at the outset
  • losses before randomisation do not lead to selection bias
3
Q

Performance bias

A
  • systematic difference in the care provided to the participant in the comparison groups other than the intervention under investigation
4
Q

Measurement bias

A
  • Systematic error in the estimate of frequency or effect due to measurement error or misclassification of the study factors, outcome factors or confounding factors
5
Q

Validity

A
  • The degree to which a measurement or test measures what it is suppoes to measure
6
Q

Repeatability/reliability

A

Ability of a measure or test to produce the same result when used repeatedly in the same person

7
Q

Sensitivity

A
  • the proportion of people who in truth have the attribute who also have a positive test
  • the proportion of people with a disease that test positive
8
Q

Specificity

A
  • the proportion of people who have a negative result and do not have the disease
9
Q

Confounding

A
  • occurs when a measure of effect is biased because of the association of the exposure with other factors that influence the outcome
10
Q

Criteria for confounding

A
  • independent predictor of outcome
  • not an intervening variable
  • associated with study facrtor - unequally distributed in the exposure group
11
Q

Practical test to know whether or not there is confounding

A
  • if there is a difference between crude and stratified measures then there is confounding, if no - no confounding
12
Q

Control of confounding at the design stage

A
  • randomisation
  • restriction
  • matching
13
Q

Control of confounding at the analysis stage

A
  • standardisation
  • stratification
  • multivariate modellinG
14
Q

Effect modification

A
  • an innate aspect of the relationship between the exposure, the effect modifier, and the outcome
  • cannot be removed through design or analysis, unlike the confounding effect