Statistics Flashcards
What is the difference between Risk and Odds
Odds is the ratio of the probability that an event will occur to the probability that it will not occur
Risk = Probability
How is risk expressed
As either a percentage or as a number between 0 and 1
What is absolute risk
the percentage or number between 0 and 1 of an event to occur
What is Relative Risk
This is the risk of an event in the treatment group compared to that in the control group
Calculated by dividing the risk in the treatment group by that in the control group
What is the Relative Risk Reduction
RRR is the reduction in risk of an event with treatment divided by the risk of an event in the control group
Relative risk reduction = reduction/control risk
Alternative method - (1 - relative risk)
What is Absolute Risk Reduction
Less misleading
Numbers instead of percentages
30/100 reduced to 5/100
Define Numbers needed to treat
The NNT is the number of people who must be treated for a given period to achieve an improvement.
It is the reciprocal of the Absolute Risk Reduction (1/ARR)
What are the limitations for NNT
You need to ensure that the choices of other drugs available
the severity of the condition and
the outcome without treatment
Adverse effects of treatment
What do NNTs not take into account
Adverse events with different treatments
Patient preference
Cost
What is a Number needed to harm - NNH
Can calculate from the absolute risk of adverse effects of treatment - useful in weighing up benefits and risks of treatment
