I don't want to throw a snarky remark out, but damn that had a bunch of weasel-ese in it. Looks kinda bad, but in a way it looks kinda good...
In addition, I found problematic the statement "The results indicate that negative results are not disappearing, but have actually become 4.3 times more prevalent since 1990. Positive results, on the other hand, have become 13.9 times more prevalent since 1990." "More prevalent", one presumes in this context, is a measurement of a subset against the total. Otherwise all you're really getting is a count of how much research is being done -- which I believe is what is being reported? That doesn't sound like a useful metric to me. Why would I care about the counts of positives or negatives when, in fact, there are only two types of things being counted? All I would really care about in this context would be their relative sizes.
There are numerous graphs plotting both the relative sizes of abstracts with positive and negative results against the total (not every abstract contains the wording they checked), e.g. Fig. 3, and graphs of their relative ratios (e.g. Fig. 4).
However, they somewhat admit that their findings are mostly spurious since checking for "p < 0.5" instead of "p = 0.04…" turned the results more or less upside down.
If you look at Figure 3 (and section 3.2.1), you'll find they're reporting the number of papers in percentage of the total number of papers. So, relative size. The increase given in the abstract is that between 1990 and 2014.
In addition, I found problematic the statement "The results indicate that negative results are not disappearing, but have actually become 4.3 times more prevalent since 1990. Positive results, on the other hand, have become 13.9 times more prevalent since 1990." "More prevalent", one presumes in this context, is a measurement of a subset against the total. Otherwise all you're really getting is a count of how much research is being done -- which I believe is what is being reported? That doesn't sound like a useful metric to me. Why would I care about the counts of positives or negatives when, in fact, there are only two types of things being counted? All I would really care about in this context would be their relative sizes.
I probably missed it.