I really like bibliometrics. Imagine my delight then, when I learnt that Google have recently introduced a new journal metric as an alternative to the impact factor. It’s called the h5 index, and you can read more about it here.
Basically, it’s equivalent to the Hirsch index, but calculated for a journal rather than an author, over a 5 year period. So, an h5 of 10 means that during the past five years a journal has published 10 articles which were each cited at least ten times (and many more articles which were cited fewer than 10 times).
I thought it would be interesting to see how this compares to the impact factor for various journals of relevance to perception researchers. So, here is a graph showing the relationship between the two metrics:
As you can see, there’s a strong correlation over the lower end of the range (approximately h5 = 12*IF), but some divergence at the top end. In particular, some journals with very different impact factors have a similar h5 index (e.g. PLoS ONE and Nature Neuroscience). I suspect this is to do with volume of papers published and scope of the journals involved (e.g. PLoS ONE publishes thousands of articles in many disciplines, so it’s not surprising it has a high h5).
Despite the many problems people have with impact factors, the hard reality is that journal metrics are useful for a range of things. I’ll be interested to see how widely the h5 index gets used over the next few years, especially given the strong correlation for the low-to-medium impact journals.
In particular, if I were Thomson I’d be very worried indeed. In the past six months or so, Google have, seemingly out of nowhere, produced viable competitors to both the Journal Citation Reports database and the ResearcherID tool for calculating an individual’s h-index. In fact, for a variety of reasons I prefer Google’s versions (they’re free, not behind an annoying paywall, much faster, more transparent, and my h-index is higher according to Google!). Although Thomson may have pioneered bibliometrics, remember that Google didn’t invent internet search – they just did it better than everyone else . . . .