Trends in published research.

<p>Stacked line graph of year of publication of identified studies. Retrospective studies are in blue, prospective studies in red and the number of RCTs indicated by the black line. [Pro: Prospective, Retro: Retrospective, RCT: Randomised Controlled Trial]. The number of publications has increased over time, including those deemed of higher quality (prospective and randomised).</p>