Past or Present Tense?
A. Wetzel et al. (2004) show a negative correlation between snow density and air temperature that explains 52% of the variance.
B. Wetzel et al. (2004) showed a negative correlation between snow density and air temperature that explains 52% of the variance.
The difference is that A uses the present tense “show”, whereas B uses the past tense “showed.”
Most of the time, I use the past tense to discuss papers that were published in the past. Recently, however, I was a coauthor on a paper where we had inadvertently mixed past and present tense in a couple of paragraphs. The reviewer picked up on this and recommended present tense. Rather than get into an argument, I went through the manuscript recently and rewrote it to nearly all present tense. I was kind of energized by doing that (new writing challenge), so I tried to adopt it with a subsequent short paper that I wrote, to further test my ability to write like this.
Present tense can make sense in this context if you think of the previously published paper existing in the present and contributing to the current discussion of the topic. If you think of it that way, it works perfectly fine, albeit it may sound different to our ears if we’re not used to it.
Bottom line: I don’t think it matters which you choose, as long as you are consistent throughout your document.
Eloquent Science has some material on verb tense in section 9.3.
Thanks to Matt Bunkers for getting me to think more about this issue.
Image from http://lilliputianjourney.blogspot.co.uk