In particular,P(D t ≤0)→0 as CV→0, so the Gaussian approximation is most appropriate for product categories with mean demand large relative to its standard deviation

HenceD t ∼ N(µ, σ 2 D) withσ 2 D =P∞ k=0 ψ2 k, therefore P(Dt ≤0) = Φ − µ σD = Φ − 1 CV ,CV := σD µ = 1 µ vuut ∞X k=0 ψ2 k, where Φ(·) is the standard normal cdf, CV is the coefficient of variation · 2022