  We consistently analyse for the first time the impact of survey depth and
spatial resolution on the most used morphological parameters for classifying
galaxies through non-parametric methods: Abraham and Conselice-Bershady
concentration indices, Gini, M20 moment of light, asymmetry, and smoothness.
Three different non-local datasets are used, ALHAMBRA and SXDS (examples of
deep ground-based surveys), and COSMOS (deep space-based survey). We used a
sample of 3000 local, visually classified galaxies, measuring their
morphological parameters at their real redshifts (z ~ 0). Then we simulated
them to match the redshift and magnitude distributions of galaxies in the
non-local surveys. The comparisons of the two sets allow to put constraints on
the use of each parameter for morphological classification and evaluate the
effectiveness of the commonly used morphological diagnostic diagrams. All
analysed parameters suffer from biases related to spatial resolution and depth,
the impact of the former being much stronger. When including asymmetry and
smoothness in classification diagrams, the noise effects must be taken into
account carefully, especially for ground-based surveys. M20 is significantly
affected, changing both the shape and range of its distribution at all
brightness levels.We suggest that diagnostic diagrams based on 2 - 3 parameters
should be avoided when classifying galaxies in ground-based surveys,
independently of their brightness; for COSMOS they should be avoided for
galaxies fainter than F814 = 23.0. These results can be applied directly to
surveys similar to ALHAMBRA, SXDS and COSMOS, and also can serve as an
upper/lower limit for shallower/deeper ones.
