Any single study's result may be invalid due to a problem with the sample of subjects picked, which may be unrepresentative of the whole population of subjects exhibiting the particular condition or symptom under study. It can also be just a coincidence, what with the standard 5% chance of that being so. So in general positive results need to be replicated in several different studies before the US Food and Drug Adminstration (FDA) will approve the drug for public consumption.
- Publishing positive studies more than once by using journal "supplements."
- Conducting a study at multiple locations and then publishing the results of the individual locations as if they were separate trials - and doing so selectively if that makes the drug look better.
- Publishing different measures of drug efficacy at differnt times to give the impression that the results published later are from a new or different study.
- Following study patients for longer and longer time periods and then publishing the results from each time period separately, again making it look like there was more than one study.
- Publishing positive results in major or more prestigious journals and negative or neutral studies in more obscure journals.
- Combining the results of multiple trials in ways that are more favorable than any individual study in its own right.