How is R-naught approximated from growth rate and serial interval in the SIR model?

Conditions

• Stated as an approximation under the simple SIR model.
• The on-screen note says it assumes exponentially distributed generation times.

Reasoning, step by step

1. Identify the growth rate $r$ and the serial interval $T_s$.
2. Multiply the growth rate by the serial interval ($r \cdot T_s$).
3. Add 1 to the product to estimate $R_0$.
4. Use the formula $R_0 = 1 + r \cdot T_s$ for the calculation.

Example

The video substitutes $r=0.15$ per day and $T_s=10$ days into the formula to compute $R_0 = 1 + 0.15 \times 10 = 2.5$.

Common misconceptions

• Treating the SIR approximation as an exact definition of $R_0$ rather than an estimate.
• Forgetting the assumption of exponentially distributed generation times when applying the formula.

Watch the explanation

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