Does Happiness have a Set Point?

Recently on Gretchen Rubin's blog, "The Happiness Project", Gretchen interviewed the ever brazen Penelope Trunk about happiness. Penelope, in her words, is "pissy" about happiness research. She doesn’t think the discussion “Am I Happy” is productive or that there is a lot of happiness in life only a lot of hopefulness. Her happiness level in life doesn’t particularly change depending on where she is in life. She has a sort of setpoint. She veers from it in the same way she veers from her regular weight the day after Thanksgiving -- She always goes back to that setpoint.

In a later post, Gretchen attempts to debunk the myth Nothing Changes a Person's Happiness Level Much. Gretchen writes:

Major life events can have strong, lasting effects on people’s happiness. For example, although people adapt quickly to marriage, it takes much longer for widows to adapt to widowhood. Losing a job, getting divorced—these kinds of events make a significant lasting impact on happiness. Adaptation varies considerably among people. Some get over changes quickly, while others take much longer to adapt, if they ever do.

This is the way I’ve come to think about this question: People are born with a natural range of temperament, but circumstances, actions, and thoughts can push people up to the top of their range or down to the bottom of their range.

I find myself agreeing so completely with Alex Lickerman at Happiness in this world's comment; I am including it in its entirety:

I've found the level of happiness I enjoy seems to fluctuate from moment-to-moment depending on how resistant I am to the vagaries of external forces pressing on my life-condition. When good things happen I tend to feel good for a while and when bad things happen I tend to feel bad for a while. But I've become convinced that if we work to increase our capacity to experience happiness, like exercising a muscle it will grow stronger, and the set point around which our happiness fluctuates will inevitably rise. But it really does seem to require diligent, consistent effort and the pursuit of a path that actually works. It also seems to me there are far more bad ways to pursue happiness than good ways.

Summary:
I am not sure if happiness has a set point, but I do know when events in my life take a turn for the worst, I’ve learned the “process of pushing myself” out of my comfort zone to search out what makes me happier always seems to help; this is the same process I’m using in my current project "Getting My Ducks in a Row". Another technique I’ve employed with success is writing entries in my gratitude journal.

Also, I don't place much credence on personal assessments such as the Authentic Happiness Inventory Questionnaire. This questionnaire requires you to answer questions by picking one statement in each group that best describes the way you have been feeling. I think these types of questionnaires are easily skewed based on how you subconsciously feel the outcome should be.

If you'd like to read more on the subject of happiness; my favorite book on the subject is Tal Ben-Shahar's Happier: Learn the Secrets to Daily Joy and Lasting Fulfillment.