It can be due to a single, highly cited paper, see the story of the Acta Crystallographica Section A Journal Impact Factor outlined in the Scientific American blog http://blogs.scientificamerican.com/information-culture/2012/05/07/understanding-the-journal-impact-factor-part-one/
Just search for "Plant Molecular Biology Reporter" in Google Scholar between year 2011 and 2012 (or just follow this link: http://scholar.google.se/scholar?q=Plant+Molecular+Biology+Reporter&hl=sv&as_sdt=0%2C5&as_ylo=2011&as_yhi=2012 ). Look at the citations for each paper and you get your answer. Its because they published a lot of papers that were cited quite a lot, many over 20 times. Kind of impressive actually...
But what about the paper in Acta Crystallographica which has been cited >23.000 times. That's what I call impressive! ;-)
Yes it is. And it would be even more impressive if Acta Crystallographica could keep on publishing articles with that impact... :-)
What I find odd is that ca. 80 % of the citations come from articles in the same journal, so called "Journal Self sites" at JCR. Very odd!
Did any of you ever submit to PMBR? You would know the answer. Count the journal self citations in articles from the recent years; you will find a minimum threshold ...
It is theoretically possible for a crowd of authors to jointly affect a small journal's IF. If so, I agree that the IF should drop again, but then we may see another small, low IF journal booming.
You means these facts, don't you (copied from the JCR):
Self Cites 847 (28% of 2985)
Self Cites to Years Used
in Impact Factor Calculation 701 (71% of 984)
Impact Factor without Self Cites 1.530
PS the graphics in the report are even more telling, regarding self-cites ...
Now it has only 2.3 in 2013/2014 recent list of Thomson Reuters (ISI) released on 29th July
Less than half of 5,319 ....... what will happen in 2015??/,,,,,,,,, Real IF
Impact Factors can be managed it seems so - and are being managed, few caught and few not
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