Scientific research could be set for a big decline because of a growing tendency to report only positive findings.
An analysis by the University of Edinburgh of more than 4,600 scientific research papers published between 1990 and 2007 found a steady decline in studies in which the findings contradicted scientific hypotheses.
"Either journals are rejecting more negative results, or scientists are producing more positives," says Dr Daniele Fanelli of the University's Institute for the Study of Science, Technology and Innovation. "It is most likely a combination of both."
Perhaps understandably, people tend to be more interested in reading scientific papers with positive results - and journals therefore tend to be more interested in publishing them.
But papers reporting null or negative findings are in principle just as useful as positive ones, even though they're less likely to be published. Omitting them from the public view means that researchers will be given a distorted picture of a given scientific field.
The trend also means that scientists - who want publication and grants - are less likely to engage in important research if they suspect that their findings are likely to be negative.
There's also a temptation to produce positive results through re-interpretation, selection or even manipulation of data.
The study examined research papers in which a hypothesis had been tested, in various scientific disciplines. Over the period studied, positive results grew from around 70 per cent in 1990 to 86 per cent in 2007.
The growth was strongest in economics, business, clinical medicine, psychology, psychiatry, pharmacology and molecular biology. Positive results were also more frequent in the US than in Europe.
"Without negative evidence in the literature, scientists might misestimate the importance of phenomena and waste resources replicating failed studies," says Fanelli.
"The higher frequency of US papers reporting positive findings may suggest that problems linked to competition are greater in the US than elsewhere."