What if you conduct a survey that asks you to rate your happiness level from 0 to 10.

How would you know that your 6 is equivalent to the other guy's 8? Nobody knows. It's impossible.

There are also cultural differences to what "happiness" even means.

Any study about happiness is likely to be bogus.

There is actually an annual UN World Happiness Report and there have been various pushes to OKR/KPI Gross National Happiness (see Bhutan for example).

https://ourworldindata.org/grapher/gdp-vs-happiness

Then it seems any study about any emotion or subjective interpretation is also bogus.