It's worth mentioning that the full version of Rohrer's framework also includes a third dimension for “context of use.” He distinguishes between the different contexts of product use for each research method: “natural use” (e.g., analytics), “scripted use” (e.g., usability tests), and “not using the product” (e.g., discovery interviews). I encourage you to explore his full framework, which categorizes 20 different UX research methods. You can find it on the Nielsen Norman Group website at http://nngroup.com/articles/which-ux-research-methods. You can see Rohrer's other publications and blog
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