Regarding Traditional Chinese herbal therapy, only few trials exist that are considered to be of adequate methodology by modern western medical researchers, and its effectiveness therefore is considered poorly documented. For example, a 2007 Cochrane review found promising evidence for the use of Chinese herbal medicine in relieving painful menstruation, compared to conventional medicine such as NSAIDs and the oral contraceptive pill, but the findings have to be interpreted with caution due to the generally low methodological quality of the included studies (as, amongst others, data for placebo control could not be obtained). The Cochrane Collaboration is an independent nonprofit organization consisting of a group of over 28,000 volunteers in more than 100 countries. The collaboration was formed to organize medical research information in a systematic way in the interests of evidence-based medicine. The group conducts systematic reviews of randomized controlled trials of health-care interventions, which it publishes in the Cochrane Library. A few reviews (in fields such as occupational health) have also studied the results of non-randomized, observational studies. The collaboration formed an official relationship in January 2011 with the World Health Organization as a partner NGO, with a seat on the World Hea th Assembly to provide input into WHO resolutions. Dysmenorrhea (or dysmenorrhoea) is a gynecological medical condition of pain during menstruation that interferes with daily activities, as defined by ACOG and others. Still, dysmenorrhea is often defined simply as menstrual pain, or at least menstrual pain that is excessive. This article uses the dysmenorrhea definition of menstrual pain that interferes with daily activities, and uses the term menstrual pain as any pain during menstruation whether it is normal or abnormal. Menstrual pain is often used synonymously with menstrual cramps, but the latter may also refer to menstrual uterine contractions, which are generally of higher strength, duration and frequency than in the rest of the menstrual cycle. Dysmenorrhea can feature different kinds of pain, including sharp, throbbing, dull, nauseating, burning, or shooting pain. Dysmenorrhea may precede menstruation by several days or may accompany it, and it usually subsides as menstruation tapers off. Dysmenorrhea may coexist with excessively heavy blood loss, known as menorrhagia. Secondary dysmenorrhea is diagnosed when symptoms are attributable to an underlying disease, disorder, or structural abnormality either within or outside the uterus. Primary dysmenorrhea is diagnosed when none of these are detected.