Introduction
Regardless of your field of interest (behaviour, growth performance...), you must first determine the reliable indicator(s) for your subject.
In most cases, you will find in the literature the scientific method to measure or to score the status of your target variable. This is considered as your “Gold standard”. The technology you use, and its development, will have to be compared to this standard.
Bio-signals coming from field data are images or sounds, or originate from sensors. Such crude information is rarely immediately useful and has to labelled (see section "How to transform the signal into valuable information").
Labelling is expensive, because it takes a lot of time in many cases.
