"A previous study on the genetics of placebo in social anxiety disorder showed that it is serotonin that is associated to placebo responsiveness and not dopamine, " he said.
The study builds on previous research which has shown the insula is involved in the onset of mood disorders.
Dr Ray and his colleague Dr Nicholas Brereton said the latest work built on previous work involving a wider study on willow varieties at the national collection at Rothamsted Research, which is the longest running agricultural research station in the world.
BBC: Sugar-rich willow can boost biofuels' green credentials
However, the Bureau of Justice Statistics, an arm of the Justice Department, cautioned that the previous study was based on a survey of current inmates in both state and federal institutions.
Like much of the previous research on coffee, the study was based on survey data -- in this case, a single questionnaire distributed in the mid-1990s -- that may provide an incomplete picture of the participants' overall health and lifestyle.
He said one former employer had reacted badly to a previous study he carried out on the subject as it had "hit international press in India which was a big market for the university".
DeBakey VA Medical Center, Houston, Texas and assistant professor of medicine at Baylor College of Medicine who has wrote several studies on diagnostic error, says that while the Hopkins study confirms previous research, malpractice data provide a limited picture.
Previous studies on the topic have largely focused on younger children, whereas this study shed light on how preteens and teens fare emotionally, socially and academically, she said.
Although it was not possible to verify the dose of vitamin C taken in the Swedish study, previous studies have demonstrated that vitamin C preparations available on the Swedish market typically contain 1000 mg per tablet.
"No previous study has allowed the evaluation of the impact of hatchery stocking activities on Penobscot river Salmon, " said Chris Lage, a graduate student working with Kornfield on the study.
CNN: Gene study seeks 'wildness' of Atlantic salmon - October 25 1999
This is the first study to highlight the effects on mortality of alcohol minimum pricing, although the Scottish government has used previous research from the University of Sheffield to claim consumption of alcohol would be reduced if prices rose.
BBC: Study claims minimum pricing cuts alcohol-related deaths
Previous research projects which have found declines in the number of new medicines focused on smaller periods of time, the study said.
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