Daniel Gilbert, author of Stumbling on Happiness, answers how it’s possible to measure something as subjective as happiness:
Measuring subjective experiences is a lot easier than you think. It’s what your eye doctor does when she fits you for glasses. She puts a lens in front of your eye and asks you to report your experience, and then she puts another lens up, and then another. She uses your reports as data, submits the data to scientific analysis, and designs a lens that will give you perfect vision — all on the basis of your reports of your subjective experience. People’s real-time reports are very good approximations of their experiences, and they make it possible for us to see the world through their eyes. People may not be able to tell us how happy they were yesterday or how happy they will be tomorrow, but they can tell us how they’re feeling at the moment we ask them. “How are you?” may be the world’s most frequently asked question, and nobody’s stumped by it.
If designing products/services based on subjective experiences is what we do, who else can we learn from? Optometrists are a start. Who else allows us to see the world through his or her eyes?