Other studies failed to reproduce this finding, and in 2011, the editor of Science formally retracted its XMRV paper while the Proceedings of the National Academy of Sciences similarly retracted a 2010 paper which had appeared to support the finding of a connection between XMRV and CFS. Research funding
United Kingdom
The lack of research funding and the funding bias towards biopsychosocial studies and against biomedical studies has been highlighted a number of times by patient groups and a number of UK politicians. A parliamentary inquiry by an ad hoc group of parliamentarians in the United Kingdom, set up and chaired by former MP, Dr Ian Gibson, called the Group on Scientific Research into CFS/ME,: 169–86  was addressed by a government minister claiming that few good biomedical research proposals have been submitted to the Medical Research Council (MRC) in contrast to those for psychosocial research. They were also told by other scientists of proposals that have been rejected, with claims of bias against biomedical research. The MRC confirmed to the group that from April 2003 to November 2006, it has turned down 10 biomedical applications relating to CFS/ME and funded five applications relating to CFS/ME, mostly in the psychiatric/psychosocial domain.In 2008, the MRC set up an expert group to consider how the MRC might encourage new high-quality research into CFS/ME and partnerships between researchers already working on CFS/ME and those in associated areas. It currently lists CFS/ME with a highlight notice, inviting researchers to develop high-quality research proposals for funding.
Differences of research participants cognitive abilities pre- and post-illness onset are naturally variable and are difficult to measure because of a lack of specialized analytical tools that can consistently quantify the specific cognitive difficulties in CFS.The frequency of neuropsychiatric and neuropsychological symptoms is increased in the population of persons with CFS; the understanding of why this occurs is unresolved. Various hypotheses have been advanced to try to explain the relationship between the cognitive symptoms and the illness. Some researchers believe psychiatric causes underlie or contribute to the illness, while other researchers believe the illness causes biochemical and sociological changes in people that produce the symptoms. Cause
The cause of CFS is unknown. Genetic and physiological factors are thought to work together to precipitate and perpetuate the condition. A 2016 report by the Institute of Medicine states that CFS is a biologically based illness, but that the biologic abnormalities are not sensitive or specific enough to be useful as a diagnosis.Because it may begin as an influenza-like illness with a sudden onset, various infectious causes have been proposed, but evidence is insufficient to support such causation. Infections proposed include mononucleosis, Chlamydophila pneumoniae, human herpesvirus 6, and Lyme disease. Inflammation may be involved. Often, the illness will follow a viral illness such as mononucleosis or gastroenteritis. Risk factors
All ages, ethnic groups, and income levels are susceptible to the illness. The CDC states that Caucasians may be diagnosed more frequently than other races in America, but the illness is at least as prevalent among African Americans and Hispanics.