Decline of the ratio between upper (σ₊) and lower (σ₋) error when adding multiple PDFs of the same asymmetry, as a function of number of PDFs added. Blue curves show five examples of functional forms that all have ; from the bottom and up are: skewed Gaussian, Weibull, lognormal, Fréchet, and loglogistic (with the latter declining somewhat slower than the others). Whereas the “usual” method of adding errors in quadrature never departs from σ₊/σ₋ = 1.5 (red), the linear (green) and quadratic (yellow) error propagation detailed in this section both perform well in terms of describing the evolution of the asymmetry.