W hich of the following do you think would make you happier: Looking younger... being cured of an illness... winning a million dollars... or changing how you think about your life as it is today?

Surprise: The latest scientific research shows that changing our circumstances accounts for only a mere 10% of happiness... while changing how we think accounts for as much as 40%.

To find out just how powerful our thoughts can be, I spoke with psychologist Sonja Lyubomirsky, PhD, author of The How of Happiness: A New Approach to Getting the Life You Want, who has devoted her career to investigating the science of human happiness.

The key she has discovered: Cultivating a sense of gratitude. Dr. Lyubomirsky explained, "Gratitude is not just saying thank you -- it has a much broader definition. Gratitude is wonder and appreciation. It is savoring instead of taking things for granted. It is looking on the bright side of setbacks. It is fathoming abundance and counting blessings. It is an antidote to negative emotions, a neutralizer of envy, avarice, hostility, worry and irritation. Gratitude involves a focus on the present moment, on appreciating your life as it is today." Here’s how to do it...

First step: Measure your gratitude level. After reading this article, take what scientists call a "pretest and post-test." On a sheet of paper that you’ll save, record the date. Now, using a scale of one to seven -- where "one" indicates the least amount possible and "seven" represents the most imaginable -- assign yourself a pretest score for each of the following...

How much gratitude you are feeling right now.

Your overall level of happiness right now.

How much gratitude you felt during the past week.

Your overall level of happiness during the past week.

Next step: Practice some or all of the gratitude-enhancing strategies below. Surprising: Doing this for as little as 15 minutes per week is effective, Dr. Lyubomirsky’s research shows. Continue for 10 weeks. Keep the exercises fresh by doing different ones in different weeks or by varying your focus -- for instance, concentrating on relationships one week, past events the next week and health issues the week after that.

After 10 weeks: For the post-test, use the scale of one to seven to rate yourself on the same four measures of gratitude and happiness as before -- two for the moment in which you are taking the test and two for the prior week. Compare these post-test scores to your pretest scores. You probably will be amazed at -- and grateful for -- the difference.

The exercises below are the key to seeing a significant change in your gratitude level. Choose the exercises that best fit your personality, interests, lifestyle, needs and schedule. Some of these strategies may seem hokey, sentimental or simplistic at first. But remember: Even a corny-sounding exercise can grow on you and end up being practiced from the heart. These techniques have been scientifically proven to work -- and there’s nothing hokey about that!

Keep a gratitude journal. Choosing a fixed day each week, record the date and time in a notebook, then write, "This week I am grateful for...." Now ponder five things for which you are currently grateful, from the mundane (your dryer is fixed) to the magnificent (the beautiful sunset)... from the past (the day you met your spouse) to the future (your grandchild soon will be born). You might focus on a talent, goal or opportunity... an enjoyable aspect of where you live or work... or people who have cared for or sacrificed for you. As you create your list, elaborate on your feelings if you wish.

Alternative: Instead of writing, simply contemplate your sources of gratitude and then voice your thoughts aloud.

Examples: Identify one thing that you usually take for granted (your strong back, your sense of humor) and focus on how it enriches your life. Or acknowledge an ungrateful thought ("My sister forgot my birthday")... then substitute a grateful thought ("She’s always there for me when it matters most") or add a but ("But I’m grateful that others remembered to acknowledge the day").

Form a gratitude partnership. Choose a friend or family member with whom to share your gratitude journey -- for instance, through an e-mail or phone call in which you share a passage from your journal or an insight from your meditation. Or introduce another person to places, activities or people you love. When you see the ordinary or familiar through the eyes of another, you appreciate it anew.

Express appreciation directly. Pick someone to whom you feel grateful -- a relative, friend, mentor, coach or teacher. Make a phone call, write a letter or pay a visit to thank that person for the role he or she has played in your life.

Show gratitude through art. Draw, paint or sculpt a representation of a person, place, object or event that has special significance for you. You’re not artistic? Make a simple collage using favorite snapshots or photos cut from magazines, focusing on those that elicit feelings of appreciation. Add relevant words such as hope, love or thanks.

Tap into your spirituality. If you’re religiously inclined, compose a prayer of gratitude. Or cultivate the ability to notice the wondrousness in everyday things (the soft rain, a sweet strawberry). Take a moment to savor the experience.

One benefit of practicing gratitude is that it starts a cycle of positive social consequences. You express appreciation for others... and then others are likely to express appreciation for you. Focusing on what you are grateful for (your health, for instance) may also encourage you to help others who have less to be thankful for -- which, in turn, gives them and you more to feel grateful for.

The happiest people have their share of stresses, trials and tragedies just as everyone else does... but they also have an inner resource of strength and contentment to draw upon in difficult times. You can develop that resource, too -- by cultivating an attitude of gratitude.