One reason is that the tool used by nearly all studies in this field — surveys asking people to self - report their happiness on numerical scales — is cheap and easy to implement. (sciencemag.org)
There is a natural numerical scale of complexity for knots, ranging from simple knots at the low energy end to more complicated ones higher up. (newscientist.com)
And then you need native speakers of each language — thousands of them — to rate how those words make them feel, using a standard numerical scale. (sciencemag.org)