Happy: late 14c., "lucky, favored by fortune, prosperous;" of events, "turning out well," from hap (n.) "chance, fortune" + -y. Sense of "very glad" first recorded late 14c. Old English eadig (from ead "wealth, riches") and gesælig, which has become silly. Meaning "greatly pleased and content" is from 1520s. Old English bliðe "happy" survives as blithe. From Greek to Irish, a great majority of the European words for "happy" at first meant "lucky." An exception is Welsh, where the word used first meant "wise."

Online Etymology Dictionary

Required definitions : happy.

Research Topic 0 (background) : The etymology of ‘happy’ (summary above).

Research Topic 1 (introduction) : US national survey, UN reports.

Research Topic 2 (current debates) : Happiness as subjective well-being – see Most People Are Happy for a good overview of this problem.

Research Topic 3 (sophistication) : what is happiness? What does it mean to be happy? Can you even actually tell at the time, or only know in retrospect?

Short answer : This question does not actually permit a short answer, since ‘very happy’ is underdefined, both to persons and as a concept. Data is available from the US national surveys, UN reports, and so on, but any given answer would have to qualify itself in accord with the concerns outlined below. Figures are also available of relative happiness – see the happy planet index for this.

Analogy : If you had never thought of happiness as a goal, would you be happier than you are today? If happiness didn’t exist until the 16^th century, were people happier or unhappier before they had a word for it?

Problems : Happiness as a concept is both poorly defined and socially evolving. It comes into English as an accident, not a state; one can be made happy by chance, but cannot find happiness, no more than one can find luck. Increasingly, this changes, until today, when happiness is the explicit goal of large sections of humanity (whereas to almost all previous generations the idea that happiness could be sought as a goal in itself would not make sense.)

As a result, You may as well say the answer is 42. The question of what happiness means, or what this would even indicate, is so diffuse and loaded that it measures nothing at all. The measure could, for example, simply indicate the level of delusion most people have. There are various good studies that show everyday false optimism actually makes us worst at predictive behaviour, and people with depressive disorders have significantly more realistic expectations – see Strunk & Adler for detail.

Still, all this poses the real problem; how can we validly measure how well people meet a standard that changes all the time, means a different thing to each person, and has a huge social cachet as an achievable ideal now that it did not have even 60 years ago?

Sophistication : Bias from questioning is extreme with poorly defined concepts. The ‘very happy’ result is almost impossible to define in a way sufficient for generating an algorithm or non-lossy selection/decision process. Moreover, the result is multimodal; if one asked ‘how happy are you with your work/ social/ personal life, and how important is each to your overall happiness?”, then there is a good chance the results would be very different, as people are not very good at identifying their preferences or feelings in the abstract, which is why we have a profession of psychiatry at all. We are much better at contextual claims that reference the world and our lives (we have difficulty assessing our weltanschauug, to be phenomenologically precise).

References :

Strunk, D., Adlera, A., 2009. Cognitive biases in three prediction tasks: A test of the cognitive model of depression, Behaviour Research and Therapy, Volume 47, Issue 1, Pages 34-40

Diener, E. & C., Most People Are Happy, Psychological Science, Vol 7, No 3, May 1996

Harper, Douglas. Happy. Online Etymology Dictionary. http://www.etymonline.com/index.php?term=happy