What does the statement mean "50% of happiness is determined by genetics"? I posted the question "Is 50% of a happiness determined by genetics?" on Skeptics but realize I don't fully understand the claim. What does it mean that 50% of happiness is determined by genetics?

Does it mean that each time a person is happy, 50% of the reason they are happy is because of genetics? How can that possibly make sense as happiness is a human construct so why wouldn't the genetic factor apply the same to other emotions like sadness?

Is an example of how genetics determines happiness, that someone is predisposed to liking chocolate, so if they're happy when eating chocolate cake, genetics is 50% of the reason they are happy? Is that the claim?

Does this mean that an unhappy person can't do that much to become happy? 

EDIT: would it be correct to say a person can change their level of happiness by +/-50%? Is this what the claim is saying? 

TL;DR does the statement mean a person has at most 50% control over how happy they are?

CBS New York reports on research presenting this claim.
The statement 50% of happiness is determined by genetics is presumably talking about heritability estimates.

It is probably talking about the percentage of variance explained by genetics. 

These estimates are commonly estimated using twin studies. For example, you administer a survey to people that ask a bunch of questions about how happy they feel. There are a variety of measures (e.g., life satisfaction measures, quality of life measures, measures of tendencies to experience positive and negative emotions). If you administer these measures to twins, some of which are fraternal and some of which are identical, you can compare the degree to which the overlap in happiness scores increases in the identical over the fraternal twins. 

A wide range of theories of well-being suggest that most people are happy most of the time. There is also theory to suggest that a person's emotional tendencies (e.g., see neuroticism, extraversion, well-being, and so on) are quite stable over long periods of time (i.e., over many years). So this does suggest, that at the very least, it is unusual for someone's emotional tendency to change dramatically over time.