Answer:
The actual impact of the training can only be evaluated by comparing the performance of employees who underwent training and those who did not.
Step-by-step explanation:
The reason is that when you conduct a post-lecture listening test then you are actually testing how much the person has absorbed the lecture which will not be reflected in the work that he will be assigned in near future. The main purpose of the training session is to make the workforce able to actually reflect the training lecture in the future work. This means if I want to increase the efficiency of the workforce then I will prefer to see whether or not the workforce which was trained have increased its work efficiency than the person who were not trained.