Evidence based education system (EBES)

1. NNT: NUMBER NEEDED TO TREAT
-Dr. SHUBHI SAXENA
DEPARTMENT OF PATHOLOGY
CENTRAL LAB, DHIRAJ HOSPITAL

2. INTRODUCTION
• Number needed to treat is one way to communicate the
effectiveness of a treatment.
• It is growing in popularity and is often reported in RCTs
and systematic reviews on therapy.
• It signifies how many patients would need to be treated to
get one additional patient better who would not have gotten
better without this particular treatment.

3. •NNT - the number of people needed to
receive an intervention before one
person gets the expected outcome!
•Depends on risks of intervention vs
outcome.
•NNT = 100 divided by Absolute Risk
Reduction (ARR)

4. Let’s try an example
• An NNT of 10 for treating sinusitis with antibiotics indicates
that 10 patients need to be given an antibiotic to get one
more patient (11th patient) better that would not have been
improved without the antibiotics.
• It does not reflect how many patients get better in total.
• This method offers one convenient way to think about how
good a particular treatment is.

5. Another example of NNT:
Does alendronate prevent hip fractures in postmenopausal women ?
The published study:
• Low bone mass density
• One or more fractures at baseline
• Alendronate 5 mg/d x 24 mo, then 10mg/d
• Outcome – subsequent reduction in hip fractures

7. Outcomes
P < 0.044
Statistically significant!
Statistical Significant does NOT equal Clinical Significant

8. Statistical Significance
• An indication that the findings are not due to chance!
• P < 0.05 means there is < 5% chance the difference between the
placebo and treated group is a chance occurrence.
• It is not an implication of clinical meaning (significance).

9. A Closer Look…
Hip fracture rate in
treated group - 1% Hip fracture rate in
control group - 2.2%

10. Absolute Risk Reduction (arr)
Placebo incidence – Treated incidence
2.2% - 1% = 1.2%
A high risk patient can reduce her risk of a hip
fracture by 1.2% from alendronate x 4 yrs

11. What is this 56% ???
Relative Risk Reduction
2.2-1(ARR)/2.2 = 56%

12. Number Needed to Treat
100/ARR = 100/(2.2-1) = 83
83 high risk women would have to be treated with
alendronate for 3 years to prevent one additional hip fracture
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