The Placebo Response Model

Additive Response: Total = Natural_History + Placebo_Effect + Drug_Effect

Response Variables

15%

Spontaneous healing or regression to the mean.

30%

Improvement from expectations and therapeutic ritual.

35%

The specific pharmacological benefit.

Key Insight

In a standard Randomized Controlled Trial (RCT):

  • Observed Drug Effect: 80%
  • Observed Placebo Effect: 45%
  • Therapeutic Gain (True Drug Effect): Only 35%

If the placebo effect is large, it becomes statistically difficult to prove the drug is actually working, even if total improvement is high.

Symptom Severity Over Time (10 Weeks)

Lower is better

Composition of Total Improvement at Week 10

Higher is better