accuracy of Thomson data

Loet Leydesdorff loet at LEYDESDORFF.NET
Fri Dec 21 02:04:59 EST 2007

Dear Stephen and colleagues, 

These (Spearman) correlations teach us, in my opinion, that the measures
covary across disciplines at the aggregate level. Since impact factors are
higher in the biomedical sciences, library usages and expert ratings would
be expected to be higher in these sciences as well?

I would expect the c/p ratio, the impact factor, and the immediacy factor to
correlate highly as one group, but total publication, total citations,
library usage, expert ratings, etc., as a second group (size related). 

As you know, my preference goes in the direction of mapping local citation
impact environments.  These can be visualized using, for example, the files
at . (See: Visualization of the Citation
Impact Environments of Scientific Journals: An online mapping exercise,
Journal of the American Society for Information Science and Technology
58(1), 25-38, 2007.) The normalization in terms of the vector space (cosine)
takes care of the size effects in the relations (links), and size can be
considered as an attribute of the nodes. 

I have no better operationalization at the moment, but I am open for

Best wishes, 



Loet Leydesdorff 
Amsterdam School of Communications Research (ASCoR), 
Kloveniersburgwal 48, 1012 CX Amsterdam. 
Tel.: +31-20- 525 6598; fax: +31-20- 525 3681 
loet at ; 


> -----Original Message-----
> From: ASIS&T Special Interest Group on Metrics 
> [mailto:SIGMETRICS at LISTSERV.UTK.EDU] On Behalf Of Stephen J. Bensman
> Sent: Thursday, December 20, 2007 10:37 PM
> Subject: Re: [SIGMETRICS] accuracy of Thomson data
> Adminstrative info for SIGMETRICS (for example unsubscribe):
> I try to do some of this in the paper posted on Dr. 
> Garfield's Web site at:
> You might want to look at the second half of the paper, where 
> I discuss 
> the Impact Factor in terms of Poisson lambdas, sampling 
> variance, random 
> error, etc.  The amazing thing to me, at least, is that 
> despite all the 
> random error and sampling variance, there is a remarkable 
> stability of 
> probability across time with Spearman rhos of 0.9 and above with high 
> respectable correlations with Total Cites, library use, and expert 
> ratings.  Most impact factors move up and down within 
> extremely narrow 
> limits across time.  I found a similar phenomenon in a paper 
> just accepted 
> by JASIST called "Distributional Differences of the Impact 
> Factor in the 
> Sciences vs. the Social Sciences: An Analysis of the Probabilistic 
> Structure of the 2005 Journal Citation Reports."   I no 
> longer own the 
> copyright and so cannot post it, but I suppose that I can let 
> you read it 
> on a private basis, if you're willing to suffer the pain of 
> reading it.  
> There is much more to the Impact Factor than meets the eye, 
> and it is an 
> extremely good measure for many purposes, if of extremely 
> doubtful use for 
> ranking purposes in the vast bulk of the cases.   
> Stephen J. Bensman, Ph.D.
> LSU Libraries
> Louisiana State University
> Baton Rouge, LA   70803
> notsjb at

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