Most of us have seen the bumper sticker: “Anyone who says money can’t buy happiness just doesn’t know where to shop.” It’s an amusing sentiment, but it provokes an important question: What exactly is the relationship between money and happiness? On one hand, there is an unquestionable link. Certainly no one would deny that having enough money to cover basic needs — to provide food, clothing and shelter — makes you happy, or at least relieves stress which leads to greater contentment. And the more money you have, the more stuff you can buy that makes you happy: that sleek iPhone 4, that fancy new car or that luxurious cashmere wrap.…