Should citations on PowerPoint slides be shortened?
I would strongly recommend against putting the full citation at the bottom of the slide. The problem is, when you are actually presenting, it will both a) make the slide look very busy as you note, and b) distract people away from the rest of the slide. Another problem is that few people will actually be able to copy down the citation (unless you linger on the slide for a very long time).
Truncated references deal with all of these problems, generally giving just enough information for a quickly scribbled note that will give the reader the ability to track down the cited paper with a little bit of work.
In addition, however, if you will be making the slides available for others to read at their leisure, there are two other good places to put references:
- A "bibliography" slide at the end, before or after where many put the funding/acknowledgements slide.
- In the "notes" field associated with the slide on which the truncated reference appears.
This is especially good when dealing with funding agencies, who like to pull slides out of your deck for presentation to their own higher-ups.
I generally agree with the sentiments already mentioned (that is, avoid putting full citations on individual slides; there is usually a better way to handle it). That said, I occasionally find myself wanting to do so for some reason, such as when I'm likely to reuse the presentation a year from now, and want to easily recall where the quoted information came from, or when I want to have the full citation available on the screen in case I'm asked about it during my presentation.
When this has been the case, I've often handled this by including a full citation, but I use a color that is very similar to the background color of the slide – perhaps a light gray if my background is white, for example – and make the font very small.
Here's an example, the slide on the left has a reference, while the slide on the right has the same reference in a more "subdued" color and smaller font:
This allows me to put the reference on the slide when I want to, but avoid having the reference be a distraction to the live audience.
My preferred way to do this is to put a short reference on the slide, perhaps not even a formatted citation (e.g. "Liu, et al. show that ..."), maybe use a numeric cite (e.g. "...[1]"), and then have a slide or two at the end listing your citations, in full form, as taken from the paper that the talk represents or will represent if the talk is discussing a work in progress. This moves the distracting stuff to the end of the talk and allows anyone who wants to go look up the citation to do so assuming you or the conference makes your slides available.
If you don't intend to make the slides available, then putting a short cite like your second example in a footnote on the slide where you first cite it is probably best. That's short enough to be remembered or jotted down by an audience member for later look up.