There is a risk of constantly changing the direction of selection by scaling traits because scaling is data dependent. We do not recommend

When selecting based on phenotypes, it is better to use Smith-Hazel weights that can be adjusted when variances change, while keeping the economic weights constant

Better still, is to apply economic weights directly to BLUPs without calculating the Smith-Hazel weights because BLUP estimation ensures that changes in variance are captured in the variance changes of BLUPs

However, if the program is already using scaled traits with the current weights, it is not advisable to just stop and assume un-scaled traits and vice-versa. There will be need to readjust the weights in order to achieve the desired selection direction

Among other assumptions, it is assumed that the economic model is constant and the current weights are correct. However, occasional restrospective index calculation using effective selection differentials may help determine how natural selection is affecting the desired selection scheme