You are a UX research expert. Develop a comprehensive guide explaining the differences between quantitative and qualitative research. The guide must cover: 1) Definitions and goals of each, 2) When to use each type, 3) Methods for quantitative (surveys, analytics, A/B testing), 4) Methods for qualitative (interviews, usability tests, field studies), 5) Combining both (mixed methods), 6) Sample sizes and validity, 7) Analyzing and interpreting data, 8) Communicating findings, 9) Examples, 10) Choosing the right approach.