Flashcards in L4 Errors in Epi Research Deck (20):
what are the two types of error?
1. errors affecting precision; RANDOM ERROR
2. errors affecting accuracy; SYSTEMATIC ERROR// BIAS
when looking at data, what kind of error produces a deviation from the true value?
errors affecting accuracy, systematic errors
when looking at data, what kind of error produce "noise"
errors affecting precision, noise
how can random error be avoided?
take large samples because greater proportion of samples will be clustered around the true population mean
what does a confidence interval indicate
the likely range of the populations mean
what statistical approach would require you to construct a forrest plot?
what are the 4 types of SYSTEMATIC ERROR
1. selection bias
2. misclassification bias
3. confounding bias
4. effect modification
what is selection bias and when does it occur
bias introduced to select units that are included in a study, occurs when selection procedures results in different relationship between exposure and outcome
how can you avoid selection bias?
random selection of study participants from study population ensure response rates are high and withdrawal rates are low amongst selected participants.
provide an example of selection bias?
estimating female population and taking sample from rugby match
what are the other kinds of selection bias? Give a brief description of them.
surveillance bias - looking in the wrong place for disease
referral bias - using referral clinics as a source of sample
non-response bias - refusal to participate
length of stay bias - longer stay in hospital = more likely to be asked to take part in trail
survival bias - apparent increase in prevalence of dx because we have methods of treating
how does misclassification bias arise?
errors in information that we record about our study
what are the four types of misclassification bias? provide brief description of each
recall bias - interviewees better at recalling events when disease has occurred
interviewer bias - interviewer privy to info
prevarication bias - subjects in study may have ulterior motives ie/ overestimating exposure for compensation claims
obsequiousness bias/ clever hans - subjects alter response to please interviewer
how can you avoid misclassification bias?
blind assessment of exposure and disease
use of complete and detailed sources of info
use of objective measures where available
describe confounding bias
distortion of true underlying relationship between exposure and outcome because of the influence of a third factor
what is a common name for confounders?
what factor is commonly a confounding variable?
what 3 characteristics are used to determine if a variable is confounding?
1. it is causally associated with the outcome
2 is is causally or non causally associated w/ exposure
3. confounding variable and exposure are on TWO SEPERATE causal pathways to the outcome
what is effect modification?
summary measure of association varies with the level of a second exposure variable