Since the 1970s, meditation and other stress-reduction techniques have been studied as possible treatments for depression and anxiety. One such practice, yoga, has received less attention in the medical literature, though it has become increasingly popular in recent decades. Yoga classes can vary from gentle and accommodating to strenuous and challenging; the choice of style tends to be based on physical ability and personal preference. Hatha yoga, the most common type of yoga practiced in the United States, combines three elements: physical poses, called asanas; controlled breath practiced in conjunction with asanas; and a short period of deep relaxation or meditation. Many of the studies evaluating yoga's therapeutic benefits have been small and poorly designed. However, a 2004 analysis found that, in recent decades, an increasing number have been randomized controlled - the most rigorous standard for proving efficacy. Available reviews of a wide range of yoga practices suggest they can reduce the impact of exaggerated stress responses and may be helpful for both anxiety and depression. In this respect, yoga functions like other self-soothing techniques, such as meditation, relaxation, exercise, or even socializing with friends.