evidence Flashcards
what is the formula for risk?
no. events of interest/total no. observations
what is the formula for odds?
no. events of interest/ no. w/o event
what is starting risk?
chance of outcome in untreated group
what is modified risk?
chance of outcome in treated group
what is relative risk reduction?
overestimates benefit as small reductions sound big
what is the value of no difference?
when the absolute risk difference = 0
when does the absolute risk dif = 0?
if no dif in values (treated vs untreated)
what is number needed to treat? (NNT)
no. px needed to treat to prevent one px from developing disease
what is the formula for NNT?
1/ARD
what is the formula for risk ratio? (RR)
risk in tx group/ risk in placebo group
what is RR if risk groups are equal?
1, value of no dif
what is an odds ratio?
ratio of odds of outcome in both groups
what is OR if odds in groups equal?
1, value of no dif
what is a confidence interval?
range of values a true population tx effect is likely to lie
how would you get value of no dif from CI?
insufficient evidence
what is understood if CI doesn’t contain value of no dif?
sufficient evidence
what is the value of no dif for ratio?
1
what is the value of no dif for difference?
0
what is an observational uncontrolled study?
researchers watch
what is a controlled cohort/case study?
observe what happens in dif situations
what are randomised controlled trials?
intervention/placebo
gives strongest evidence
what is a case report/series?
report on px w/ outcome of interest
no control
what is a cross sectional study?
study of people w/ disease + control group w/o
what is a cohort study?
establish group, measure exposures, follow up, identify those that develop disease
