Goodness-of-fit test implemented following Gelman et al. (1996). A distribution of χ² values for 500 forward simulations at the MAP cosmology is evaluated from a χ² function characterised by a Gaussian likelihood defined by a numerical covariance. The vertical dashed line indicates the χ² for the MAP when analysing the real KiDS-1000 data vector. The solid blue line shows the histogram upon the application of a smoothing kernel. Since the data’s χ² falls near the mean and the mode of the χ² distribution from random realisations of the anisotropic systematics model, we conclude that the model evaluated at the MAP cosmology provides a good fit to the data, i.e. the data is a feasible realisation of the model.