According to medical scholar John Ioannidis, most published research findings are wrong.

These flawed findings, for the most part, stem not from fraud or formal misconduct, but from more mundane misbehavior: miscalculation, poor study design or self-serving data analysis. "There is an increasing concern that in modern research, false findings may be the majority or even the vast majority of published research claims," Dr. Ioannidis said. "A new claim about a research finding is more likely to be false than true." From Science Journal - WSJ.com.

Dr. Ioannidis’s 2005 essay ‘Why Most Published Research Findings Are False’ “remains the most downloaded technical paper that the journal PLoS Medicine has ever published”.

The lesson from his research is that findings must be replicated in several different studies before the results are believed.