1. Calculating Absolute Effect based on OR

$$N=1000*(ACR-\frac{OR*ACR}{1-ACR+OR*ACR})$$

2. Calculating Absolute Effect based on RR

$$N=1000*ACR*(1-RR)$$

3. Calculating Absolute Effect based on HR

$$N=1000*[(1-ACR)^{HR}-(1-ACR)]$$

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Explanation:

• The absolute effect is calculated based on the relative magnitude of an effect (relative effect measure) and baseline risk (assumed control risk or ACR).
• ACR (Assumed Control Risk) refers to the incidence rate in the control group. It can be estimated from the study with the largest control group or calculated by pooling events and total numbers from all included studies.
• Clinical Explanation
  • If the result is positive, interpret as "N fewer people per 1000 experience the outcome."
  • If negative, interpret as "N more people per 1000 experience the outcome."
  • For instance, if RR = 0.6 and ACR = 0.061, the result 𝑁 = 24, which indicates that "24 fewer people per 1000 experience the outcome."
• Rounding: Round the result to the nearest whole number.
• Confidence Intervals: For confidence intervals, direct input the upper and lower bounds into the formula.