Interpreting the evidence 1 Flashcards
how do you calculate NNT
1/ ARD
how do you calculate Absolute risk reduction
risk(group1)- risk (group2)
how do you calculate relative risk ratio
risk (group1)/ risk (group2)
what are odds ratios used for
case control studies or observational studies and regression models
how do you calculate odds ratios
number of smokers/ number of non smokers = odds of being a smoker
odds ratio = odds smoker if case/ odds smoker if control
=odds of being a smoker if you died by 60 are 6 times the odds of being a smoker in the group who lived
how do you calculate standard deviation
sum of squared deviations from the mean / n-1
square root the answer
what is standard error of the mean
the variability of means from different samples
a large SE indicates that there is much variability in sample means
SE is always smaller than SD because there is less variability between sample means than individual values
can also calculate the standard error of odds ratio
larger samples lead to a smaller SE
how do you calculate SE
SE= SD / sq root of n
what is a confidence interval
gives a range of values, estimated from the sample data which is likely to include the mean
a range of values within which we are 95% confident the true population mean lies
tells us whether observed differences are likely to be due to chance alone or a true effect
