Impact factors have been increasing by 2.6% per year, on average. While this is lower than most economies’ inflation rates, it’s indicates a growing economy. But is the growth caused by supply or demand?

In a draft paper from the academics behind the Eigenfactor, the reasons behind impact factor inflation are nicely explored.

Essentially, the researchers find that the source of impact factor inflation is the gradual increase in the number of reference citations in articles. It is essentially inflation caused by increases in demand (each published paper cites more articles), and not supply (there are more papers citing articles).

For instance, if there had only been more articles published (supply), there would have been some deflation of impact factors because citations would have spread out over more papers. The authors calculate that the longer reference lists are the major factor contributing to impact factor inflation.

In fact, as the authors explain, more papers alone would be self-neutralizing relative to impact factor inflation:

The basic intuition underlying this result is as follows: first, note that larger fields do not have higher impact factors by shear virtue of their size. While more articles are published in larger fields and thus more citations are given out, those citations are shared among a larger pool of papers.

In short, more papers alone dilute impact factors. If you’ve ever analyzed a set of impact factors, you see this on the micro level. It’s interesting to see calculations showing their effects on the macro level, as well.

One other variable the authors identify as contributing to impact factor inflation is the churn and burn and creativity of the journal economy. During the years studied (1995-2004), journals with low impact factors were shut down, and new journals entered. The journals that failed had low impact factors. The new entrants came in with and attained impact factors lower than average as well, but grew at a rate nearly twice as high (6.0%) as overall inflation. Like the money economy, this “NASDAQ” of journals fuels growth with smaller but faster ascendancies.

Impact factor inflation makes a lot of sense, and isn’t disturbing to me in the least. It’s good the scholarly economy is growing with modest inflation. There are more scientists and researchers producing more papers and citing more papers. The availability of information is apparently quite high, and researchers have many outlets for their reports.

Overall, I view this as good news. Do you?