Summary: For most teams, approaching persona creation qualitatively is the right balance of effort vs. value, but very large or very small organizations might benefit from statistical or lightweight approaches, respectively.
Personas used in UX work are a quick, empathy-inducing shorthand for our users’ context, motivations, needs, and approaches to using our products. They are meant to help us focus on what matters most to our users and put ourselves in their shoes when making design decisions. Because of this, they must always be rooted in a qualitative understanding of users and reflect the what and why that drives them. They should not be based on (often dubious) correlations between different demographic or analytics variables.