Bias on the mean redshift averaged over the 18 photometric noise realisations in the LSST/Euclid case. We assume a SOM training sample, and the different symbols correspond to various fractions of failure introduced in the spec-z training sample. Left and right panels: correspond to different assumptions on how to distribute the catastrophic failures in the spec-z measurements: uniformly distributed between 0 < z < 4 (left) and assuming the failures are caused by misclassified emission lines (right). Upper and lower panels: correspond to the direct calibration and de-biasing methods, respectively.