I answer the question "Did training work?" with facts, evidence and data

Finding facts, evidence and data for the impact of training and learning may not be easy but it's possible.

Find one thing about a person's behavior or performance you can attribute to training and learning and let that lead to the facts about impact.

If someone were to ask, “Do you have evidence for the impact of your training programs?”, what would your answer be? 

Don't be afraid when the facts tell you training didn't work. Be afraid of not doing anything with what the facts tell you.