10 marker Flashcards
what are randomised control trials
prospective studies that measure an intervention by comparing to a control
randomisation enables fair comparison
advantages of randomised control trial
intervention and control groups will be similar in all respects except the intervention minimising selection bias and confounding
if the participants are “blind” to the treatment allocation, reporting bias is minimised; if the investigators are “blind” to the allocation, observer bias is minimised
carry less risk of bias and confounding than other study designs and so can provide powerful evidence of causal relationship between the intervention and the outcome
multiple outcomes can be examined
the incidence rate of the outcome can be measured
disadvantages of RCTs
expensive to conduct- may require large study team, at several sites and may require long follow up period
intervention studies are impossible sometimes for ethical or logistical reasons
recruitment is difficult and time-consuming
trials can take years
features of randomised control trials
every participant has a known chance of being allocated to either treatment groups
the allocation sequence is not known to anybody
RCTs can be blind which means either the participant, clinical team or research team don’t know who has which intervention
what is a cohort study
is when the exposure status is already defined before the outcome is assessed
different types of cohort study
prospective- measures risk factors through follow up, records must be maintained well, time consuming, expensive
retrospective- outcome of interest examined today in individuals with a history of exposure, faster answers, cheaper, must have consistent quality of records
why do we need cohort studies
infrequent/ rare exposures
multiple outcomes related to infrequent exposure
good for establishing temporal sequence
interested in risk over time
advantages of a cohort study
temporality- exposure precedes outcome
no recall bias
can study multiple outcomes associated with rare exposures
can estimate all measures of incidence and effect
disadvantages of cohort study
requires large investment of time
requires large sample size
reproducibility is hard
loss to follow up
inefficient for rare diseases
uncontrolled confounding
bias in cohort studies
selection bias
information bias
confounding
what is a case control study
selected cases and controls and measure exposure in cases vs controls
advantages of case control
good for rare outcomes
multiple exposures
time varying exposures
disadvantages of case controls
would require large number of cases
recall bias
features of case control studies
the more controls the more power (up to 4)
case selection needs to be done correctly- can cause selection bias or information bias
prevalent vs incident cases
prevalent cases- existing cases of disease, increases sample size, reflects determinants of disease onset or duration
incident- newly diagnosed, lower sample size, reflects determinants of disease onset
