validity did not significantly affect this conclusion. The results of reviews are generally negative or only weakly positive, and reviewers consistently report the poor quality of trials. The finding of Linde et al. that more rigorous studies produce less positive results is supported in several and contradicted by none. Statements by major medical organizations Health organizations such as the UK's National Health Service, the American Medical Association, the FASEB, and the National Health and Medical Research Council of Australia, have issued statements of their conclusion that there is "no good-quality evidence that homeopathy is effective as a treatment for any health condition". In 2009, World Health Organization official Mario Raviglione criticized the use of homeopathy to treat tuberculosis; similarly, another WHO spokesperson argued there was no evidence homeopathy would be an effective treatment for diarrhoea. They warned against the use of homeopathy for serious conditions such as depression, HIV and malaria. The American College of Medical Toxicology and the American Academy of Clinical Toxicology recommend that no one use homeopathic treatment for disease or as a preventive health measure. These organizations report that no evidence exists that homeopathic treatment is effective, but that there is evidence that using these treatments produces harm and can bring indirect health risks by delaying conventional treatment. Explanations of perceived effects Science offers a variety of explanations for how homeopathy may appear to cure diseases or alleviate symptoms even though the preparations themselves are inert: The placebo effect – the intensive consultation process and expectations for the homeopathic preparations may cause the effect. Therapeutic effect of the consultation – the care, concern, and reassurance a patient experiences when opening up to a compassionate caregiver can have a positive effect on the patient's well-being. Unassisted natural healing – time and the body's ability to heal without assistance can eliminate many diseases of their own accord. Unrecognized treatments – an unrelated food, exercise, environmental agent, or treatment for a different ailment, may have occurred. Regression towards the mean – since many diseases or conditions are cyclical, symptoms vary over time and patients tend to seek care when discomfort is greatest; they may feel better anyway but because of the timing of the visit to the homeopath they attribute improvement to the preparation taken. Non-homeopathic treatment – patients may also receive standard medical care at the same time as homeopathic treatment, and the former is responsible for improvement.