There is one inalienable truth about happiness. Grumpy old men, and women, are not grumpy whatsoever -- contrary to popular myth. In fact, this truth remains the most contrarian of all research on happiness, and, to the best of my knowledge, is still the most evidence-based.

In a brilliant study published in 2010 in the Proceedings of the National Academy of Sciences, Arthur Stone and colleagues interviewed over 340,000 people in the United States by telephone to ask about how happy they were. The survey asked each person to rank overall life satisfaction on a 10-point scale and to answer six yes-or-no questions about enjoyment, happiness, stress, worry, anger, and sadness.

What the researchers found surprised them. Levels of stress and anger decline progressively and significantly after people pass through their early 20s. This is not a story about the feeling of emancipation that comes with graduating from college or paying for your own cellphone plan. We humans shed stress and anger bit by bit as we age.

Over 50 and Smiling?

When it comes to the feeling of worry, it follows a slightly different trajectory. Worry rises after age 18, but then falls again after 50. Perhaps by that time all your anxious worries have already materialized -- the career that never reached the heights you once imagined; the marriage that fizzled; the house that foreclosed; the friends who betrayed you; the children who turned out less than perfect. After age 50, there is nothing further to worry about and so one becomes increasingly happy. Or at least that's one explanation.

If true, this is of great significance for managers in recessionary times. Many over 50 have been thrust into long-term unemployment. Yet thanks to this new study, we now have powerful data to fight age discrimination in the workplace. Older workers are happy workers, and happy workers are more sensitive to client needs. Leaders, take note.

The study followed a careful methodology. All the various feelings were measured using tools called "Hedonic WB" and "Global WB." WB stands for well-being. This reflects one's own subjective view of the experience of well-being. External realities don't matter. You could be living in squalor (as long as you have a phone and can be reached in order to be surveyed) and you still apparently feel more and more content as you age. Amazing when you consider that by age 85 (the happiness apex apparently) one's physical health is generally not top notch.

Why would people be happier when they get older? Is it because they have accumulated material goods over their life span? Do riches make people happier? Apparently not. Being a man or a woman didn't make a difference, being single or partnered didn't make a difference, being employed or not didn't matter and neither did having children at home. In other words, outside circumstances didn't affect the outcome as far as the researchers could tell. Contentment is a state of mind.

Maybe world views change with maturity. You get wise and realize, by the time you reach your 80s, that possessions and earthly glory don't count. It's the emotional-spiritual dimension that really matters.

But there may be another explanation still. Perhaps the progressive elimination of crucial nerve cells in the brain have obliterated bad memories so there's nothing remembered worth worrying about? Nerve cells die at random, I was taught. But maybe that's not true. Maybe the nerve networks that record good times stay intact longer than those others that hold awkward, humiliating, depressing moments that you have ruminated over so often that the circuits are worn from overuse, burnt out, and the bad memories have melted away forever.

Whatever the reason behind the study's results, the news is good for older people (and something to look forward to even if you're young). By the time you hit 85, you'll be more satisfied with yourself than you ever were. Bob Dylan was right. You'll be so much younger then, you're older than that now.

This essay is adapted and updated from the author's 2010 blog at Longwoods.com

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• 20. Honduras

  In Honduras, 79 percent of respondents reported positive emotions.

• 19. Indonesia

  In Indonesia, 79 percent of respondents reported positive emotions.

• 18. Oman

  In Oman, 79 percent of respondents reported positive emotions.

• 17. Kuwait

  In Kuwait, 79 percent of respondents reported positive emotions.

• 16. Denmark

  In Denmark, 79 percent of respondents reported positive emotions.

• 15. Ireland

  In Ireland, 80 percent of respondents reported positive emotions.

• 14. The Netherlands

  In the Netherlands, 80 percent of respondents reported positive emotions.

• 13. Malaysia

  In Malaysia, 80 percent of respondents reported positive emotions.

• 12. Colombia

  In Colombia, 80 percent of respondents reported positive emotions.

• 11. Canada

  In Canada, 80 percent of respondents reported positive emotions.

• 10. Costa Rica

  In Costa Rica, 81 percent of respondents reported positive emotions.

• 9. Ecuador

  In Ecuador, 81 percent of respondents reported positive emotions.

• 8. The Phillipines

  In the Philippines, 82 percent of respondents reported positive emotions.

• 7. Guatemala

  In Guatemala, 82 percent of respondents reported positive emotions.

• 6. Thailand

  In Thailand, 83 percent of respondents reported positive emotions.

• 5. Trinidad & Tobago

  In Trinidad and Tobago, 83 percent of respondents reported positive emotions.

• 4. Venezuela

  In Venezuela, 84 percent of respondents reported positive emotions.

• 3. El Salvador

  In El Salvador, 84 percent of respondents reported positive emotions.

• 2. Paraguay

  Paraguay tied with Panama for the most positive emotions of all the surveyed countries, with 85 percent of respondents reporting positive emotions.

• 1. Panama

  Panama tied with Paraguay for the most positive emotions of all the surveyed countries, with 85 percent of respondents reporting positive emotions.

• How to Become Happier

  Learn how to become happier with these scientifically-proven mood boosters.

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