> the study doesn't measure happiness vs performance, it measures "how do you rate yourself" vs "the army's selection process for awarding medals".

The author explains that happiness is subjective:

> The behavioral science literature often refers to happiness as subjective well-being because the meaning of happiness varies in different contexts

...and then proceeds to delineate how psychology defines happiness:

1. a person’s own assessment of their satisfaction with life;

2. how much positive emotion [...] they experience;

3. and how little negative emotion [...] they experience

So yeah, self-rating is an important factor to measuring happiness.