Economists (and actuaries) like to measure things.
The easier to measure and the more reliable the measure, the more we like to measure it. This is not unlike the drunk looking for his keys under the street lamp because that’s where the light is even if it isn’t where he dropped the keys.
Sometimes the most important things to measure are very difficult to measure reliably. Happiness is one of these things. Economists have been trying to measure this for decades with interesting, counter-intuitive and sometimes contradictory results.
Recent research suggests that maybe money does make people happier after all.