Abstractions are critical to human thinking in science. But not only reification is very different, you can't measure happiness even if you want to. You'll always have to go 'happiness as defined ...' or resort to people self reporting their feelings. Which is fine - I always ask my kids how they feel. I just understand that not only kids and adults may change how they feel next hour but that those feelings are unreliable. If you have kids of your own, you know how many 'tragedies' they lived through by the age of 6.