Rapid Responses are wonderful
The paper raises the interesting issue of whether the main peer-reviewed papers have evolved in step with the publishing medium.
But rapid responses, are definitely a huge change from the situation before the online world came into existence - rapid responses are much more numerous than the earlier printed letters, and are indeed rapid. They allow for an almost immediate analysis of 'intricate and technical issues' which arise from the original paper. And although I usually try to restrain myself from doing this, it is possible to effectively 'debate a point almost in real time with another individual' using rapid responses, as I did recently during discussion of the Montgomery ruling.
I also suspect, that rapid responses can 'escape from the restraints of evidence-based research', and from the possible restrictive effects of peer review [which might tend to 'reinforce uniformity'], and therefore rapid responses allow for some really interesting discussions of issues 'at the edges of medicine': for example where medicine and law interact, or where patients and clinicians might see things significantly differently. 'Primary' papers are usually either a description of experiment and observation, or describe 'one opinion': but rapid responses, are much more of a 'debate'. Personally I find experiment and observation informative - but I sometimes find debate, fascinating as well as informative.
Rapid responses, are wonderful !
Competing interests: No competing interests