Yes! These tools actually work well together. The 5 Whys and the Ishikawa (Fishbone) Diagram are two of the best tools to use in the Analyze Phase. They both enable “Structured Brainstorming.” The Ishikawa allows a group of people to brainstorm potential root causes to a problem, and then the 5 Whys helps you move past symptoms to what might be the underlying root causes. The next step would be to collect data, make observations or conduct tests to verify the true root cause. Until verification, these are just hypotheses. Hypothesis testing would be a great options if data or observation doesn’t make it obvious.