This is not always a product of financial pressure. Some early studies accurately report a large effect on a specific population – such as on people in a certain age bracket – but later research shows the population as a whole are less responsive.
These early, but exaggerated, papers were likely to be highly cited. After all, if you are not only the first to study something, but make big claims, other people will take notice and respond, even if it is only to show you've stuffed up. With career advancement often dependent on how often a paper is cited, there is clearly a danger that scientists could be rewarded for being wrong.
Early career researchers are more likely to publish exaggerated results, Fanelli found. It's not clear whether this reflects inexperience, the pressure on younger scientists to get themselves into more secure positions, or simply because those scientists who do shoddy work get weeded out.
Small teams are more prone to publish work that subsequently gets discredited than larger collaborations, but there Fanelli found no relationship between the volume of publications an author is involved in and the credibility of their work.
Authors who had previously or subsequently had a paper withdrawn were particularly prone to report large effect sizes, although whether this indicates they are more likely to be sloppy, or are actually fraudulent, has not been settled.