Fig 1. The simulation scenario.

γ ₀ = 1 for all simulation scenarios. The over-dispersion parameter κ is set to be 1 for all ZINB simulation scenarios. β ₀ reflects the log odds of zero inflation in the unexposed group, and is equal to {−1.386, 0, 1.386} for the {20%, 50%, 80%} of zero inflation in this group. β ₁ reflects the change in log odds of zero inflation when changing from unexposed to exposed group. The corresponding values of β ₁ of {−5%, 0, +5%} changing in the zero inflation are {−0.349, 0, 0.287}, {0.201, 0, 0.201}, and {−0.287, 0, 0.349} for 20%, 50% and 80% of the zero inflations in the unexposed group, repsectively.