The first tactic is to try active listening where you repeat back to them what you understood as their answer and let them explain if that is what they meant. "Did I understand correctly?" is an easy question to get them to respond. "Could you explain your answer for me in another way?" is another question to get them to expand an answer. I assume the questions you ask them are all open-ended questions, so maybe just a simple "Would you clarify that statement for me?" would be sufficient. Another tactic I use is quiet silence waiting for them to develop their answer more fully which works with many people as silence can be uncomfortable and they often fill it. A third tactic is to ask the question in another way as the person may not have understood exactly what the question included. Nuances in language can have a huge effect on how someone else understands a question and what kind of answer is required.