3B. Probability, Odds and Risk Flashcards
what are odds?
the number of patients who achieve the end point against the number of patients who did not achieve the end point
what is the equation for odds?
Odds = number of patients achieving end point / number of patients NOT achieving end point
what is the equation for the odds ratio?
Odds ratio = odds for treatment group / odds for control group
what does it mean if the Odds ratio is less than 1?
it means fewer people have recovered from treatment
what does it mean if the Odds ratio is more than 1?
it means that more people have recovered from treatment
what is risk fundamentally?
a probability
what is the equation for risk?
risk = number of patients achieving end point / total number of patients
what is risk ratio
risk ratio = risk for one group / risk for another group
what does it mean if risk ratio is 1
means that both groups have the same amount of risk
what does it mean if risk ratio is greater than 1
means that the risk of the group on the top of the fraction was the greater risk or probability.
what does it mean if risk ratio is less than 1?
it means that the risk of the group on the bottom of the fraction was the greater risk or probability
what is absolute risk?
the event rate of something happening
what is absolute risk reduction?
the difference between the treatment risk and the control risk.
OR
control event rate - Experimental event rate
(treatment risk is the same as experimental event rate and control risk is the same as control event rate)
what is relative risk?
the treatment risk of getting ill as a proportion of the control risk of getting ill
what are the 2 forms of the relative risk equation
Experimental event rate / control event rate
OR
treatment risk of remaining ill / control risk of remaining ill
