RR – Relative Risk:
RR – Relative Risk Risk of an event relative to exposure Event can be disease or death Exposure can be to exposure to therapy or environmental exposure
Here’s the 2x2 table again:
Here’s the 2x2 table again interesting outcome Present Absent total Exposed a b a+b Not exposed c d c+d Total a+c b+d a+b+c+d
How to calculate the RR:
How to calculate the RR interesting outcome Present Absent total Exposed a b a+b Not exposed c d c+d Total a+c b+d a+b+c+d [ a/( a+b ) ] / [ c/( c+d ) ] a/( a+b ) c /( c+d )
Example: “July Effect “ :
Example: “July Effect “ Review “July Effect”: Impact of the Academic Year-End Changeover on Patient Outcomes. A Systematic Review John Q. Young , MD, MPP; Sumant R. Ranji , MD; Robert M. Wachter , MD; Connie M. Lee , MD; Brian Niehaus , MD; and Andrew D. Auerbach , MD, MPH
“July Effect” and mortality:
“July Effect” and mortality interesting outcome (mortality) Present Absent (dead) (not dead) total Exposed a (36) b (964) a+b (1000) (July admission) Not exposed c (3) d (997) c+d (1000) (admission out of July) Total a+c b+d a+b+c+d [ a/( a+b ) ] / [ c/( c+d ) ] 36/1000 3/1000 =12
What does the RR mean?:
What does the RR mean? = 1 no difference > 1 more likely to occur in test group < 1 less likely to occur in test group [a/( a+b )] / [c/( c+d )]
RR – remember::
RR – remember: Use in RCT and cohort studies Need group of people with and without exposure Cannot use if case-control study No information about the actual risk
Slide 9:
That’s it. Thanks.