How would farmers determine if training, instead of some other reason, was responsible for the failure of new agents?

Explanation:

In order to make this determination, the farmers would need to design an experiment and isolate the "training" as the single variable in the experiment. They can accomplish this by selecting a handful of individuals and giving them training. Then making sure that all of the agents (both trained and untrained) are placed in the same environment with all the same constants and once they are done compare the results. If the un-trained agents provide better results than the trained agents under the exact same circumstances then the "training" would be determined as being the main reason for the failure.