An endangered species is a species of organisms facing a very high risk of extinction. The phrase is used vaguely in common parlance for any species fitting this description, but its use by conservation biologists typically refers to those designated Endangered in the IUCN Red List, where it is the second most severe conservation status for wild populations, following Critically Endangered.
I measure my happiness 2 ways. 1  Through a (random and irregular) process of self reflection.  2 Catching myself being happy and remembering the last time I caught myself being happy and trying to determine the time between them.
The only thing you can measure is a change in behavior. If there is no behavior change, there is nothing to measure. (You might try sentiment analysis, but that is only a proxy variable for behavior change. What would be the point of making people feel differently if they did not act differently as a consequence.)