Frost stress distribution before and after the 1987/1988 temperature shift and for the two stress resistance traits −13 °C and −23 °C and for all dates of sowing, for rates of acclimation. Green area corresponds to the common area of the two distributions. Cyan color indicates higher probability that frost stress index occurs during period 1961–1987 while for the yellow color it is the reverse. As the frost stress distributions are zero-inflated and left heavy-tailed, a robust Bayesian estimation following the method described in Kruschke (2013) is use to test the difference. The 95% Highest Density Interval (HDI) is a useful summary of where the bulk of the most credible values falls. When the difference is significant means that the 95% HDI interval does not include zero (no difference between periods).