Rows 1−3: kurtosis value (from a moments analysis) versus the κ index of a modelled spectral line, showing differences in the inferred values of kurtosis due to a) spectral pixel size; b) chosen wavelength range; and c) skewness. In each plot, ideal parameters are used and one variable is changed (plot legend) to match the EIS value. Row 4: κ index found from line fitting versus the κ index of a modelled spectral line. Line skewness can change the values of κ index found from line fitting. Row 5: kurtosis versus modelled κ index, as rows 1−3, but now the collective effects of all sources of uncertainty are shown together using the EIS spectral pixel size (Δλ = 0.022 Å), the observed wavelength range of λ₀ ± 0.2 Å and a skewness equal to 0, for different noise levels of 0%, 2%, 5%, and 10%.