Knowing NNT

Introduction to Number Needed to Treat (NNT)

  • Host: Anthony Croco

  • Importance of understanding NNT in healthcare literature.

Definition of NNT

  • NNT: The number of patients needed to expose to an intervention to achieve a positive outcome in one patient.

Example to Illustrate NNT

  • Scenario Setup: Two groups (Control and Treatment), each with three patients.

    • Control Group Outcomes: 1 good outcome, 2 bad outcomes.

    • Treatment Group Outcomes: 2 good outcomes, 1 bad outcome.

    • Observation:

      • Both groups have a third of patients with good outcomes independent of the treatment.

      • Identifies patients who benefit from treatment (those in Control with bad outcome and Treatment with good outcome).

Calculation of NNT

  • Formula: NNT = 1 / Absolute Risk Reduction (ARR)

  • Absolute Risk Reduction:

    • Defined as the event rate in the Control group minus the event rate in the Treatment group.

    • Using the example:

      • Control Group Bad Outcome Rate: 2/3

      • Treatment Group Bad Outcome Rate: 1/3

      • ARR = (2/3) - (1/3) = 1/3 or 33%.

  • NNT Calculation:

    • Plugging into formula: NNT = 1 / (1/3) = 3.

    • Interpretation: For every three patients treated, one benefits.

  • Note: NNT does not provide insights on the outcomes of the other two patients.

Assessing the Quality of NNT

  • Lower NNT values are generally considered better.

  • Importance of context when interpreting what constitutes a "good" NNT.

Comparative Examples

  • NNT of 5:

    • Benefit: One less episode of flatulence per day.

    • Risk: 50% chance of fatal myocardial infarction.

    • Conclusion: Not a favorable outcome despite a low NNT.

  • NNT of 50:

    • Benefit: One less hospital admission.

    • Cost: $1 million per dose, requiring $50 million to prevent one admission.

    • Conclusion: Not cost-effective.

  • NNT of 50,000:

    • Benefit: One less mortality, no adverse effects, and treatment is free.

    • Conclusion: Favorable despite high NNT.

Conclusion

  • Key takeaway: The value of NNT is context-dependent.

  • Consideration of benefits, risks, and costs of therapy is crucial when interpreting NNT.

  • Encouragement to evaluate critically and draw personal conclusions about NNT in the context of healthcare.