Evaluating Therapy Flashcards
1st column of table in RCTs
Treatment
Placebo
Total
2nd column of table in RCTs
Outcome present
A
C
A+C
3rd column of table in RCTs
Outcome absent
B
D
B+D
4th column of table in RCTs
A+B
C+D
A+B+C+D
1st row of table in RCTs
Outcome present, outcome absent
2nd row of table in RCTs
Treatment, A, B, A+B
3rd row of table in RCTs
Placebo, C, D, C+D
4th row of table in RCTs
Total, A+C, B+D, A+B+C+D
What is the control event rate (CER) in placebo group?
Frequency of event
Calculation of CER
C/(C+D)
What is Experimental event rate (EER)?
Frequency of event in treatment group
Calculation for EER
A/(A+B)
Odds of the event of interest in treatment group?
A/B
Odds of event of interest in placebo group?
C/D
Odds ratio?
(A/B)/(C/D)
Another name for absolute benefit increase?
Absolute risk reduction
Calculation for absolute risk reduction
EER - CER
Calculation for relative risk
[A/(A+B)] / [C/(C+D)]
or
EER/CER
Another name for relative benefit increase
Relative risk reduction
Calculation for relative risk reduction
ABI/CER
or
(EER-CER)/CER
or
RR-1
What is NNT?
Number of patients who would have to receive treatment for one of them to benefit
Calculation of NNT
100/ARR
Unit of NNT
Percentage
Calculation for NNH (number needed to harm)
100/Absolute risk increase
Unit for NNH
Percentage
What is considered a significant value for NNT
<10
What does NNT of 1 mean?
Everyone gets better with treatment, no one gets better with controls
What value of NNT represents effective therapies
2-5
Difference between trial participants and clinical population
Differences in baseline risk rates
What do you need to change if applying RCT data to your own clinical patients?
CER - baseline risk in group w/o intervention
What is the name of the new CER for your own clinical sample?
Patient expected event rate - PEER
What is the PEER?
Control event rate in local population in which intervention is planned
How do get a new ABI from PEER?
RBI x PEr
How to get new NNT from PEER
1/ABI(new)
How to get new NNT from f value?
NNT(old)/f value
What is the f value?
Susceptibility of a local population to a particular outcome
