Poster presented at Medical Library Association annual meeting, May 2010Describes an algorithm for bibliographic analysi

Spore, Stuart

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P-Index, A Novel Algorithm for Bibliometric Analysis
Stuart Spore, NYU Health Sciences Libraries, New York University School of Medicine
The chart at the center illustrates relationships among publication numbers, H-index, 
and P-index values for  ve age-based cohorts of faculty at the NYU School of 
Medicine. From the left, members of cohort A are 60 or more years old, cohort B, 
50-60 years old, cohort C, 40-50 years old, cohort D, 30-40 years old, and 
cohort E, less than 30 years old.
What is the H-index?
The H-index is a widely-used measure of an author’s number of publications and the 
number of times that each of those publications is cited elsewhere. The value of h is 
equal to the number of papers (N) by a given author that are cited N or more times in 
other publications. For example, the publication set below generates an H-Index of 6; 
counting down from the top item #6 is  rst item where item # is greater than the 
number of times cited.
Item # Citation Times Cited
1 Journal of Cement v.3(4):35 23
2 Journal of Concrete v.12(1):3 20
3 Journal of Hard Substances v.1(1):1 16
4 Cement Weekly v.30(52):25 10
5 Journal of Cement v.2(1):12 6
6 Journal of Asphalt v.33(12):6 3
7 Journal of Cement v.1(2):3 0
8 Cement Weekly v.16(1):1 0
9 Journal of Asphalt v.2(3):12 0
10 Journal of Concrete v.6(6):6 0
What is the P-Index? 
The P-index is a metric developed to measure faculty publishing productivity at 
NYU School of Medicine. Each publication is assigned a value of the impact 
factor of the host journal plus 1.   Articles published in journals with no impact 
factor are arbitrarily given a value of 0.05. The P-index is the sum of all the 
values, for example:
Journal Impact Factor P-Value
Lancet neurology 14.270 15.270
Neurology forum n/a 0.050
Pediatric neurology 1.505 2.505
Reviews in Neurological Dis-
eases
n/a 0.050
Revue neurologique 0.508 1.508
P-Index 19.383
Books, chapters, and minor journal articles (e.g. meeting abstracts, letters, 
editorials) are excluded from P-index calculations.
Do P-index and H-index agree? 
The answer is a (very) rough yes. Both P-index and H-index values rise and fall 
together, although the numbers themselves obviously diverge. The range of possible 
values is much wider for P-index than H-index, (0-2250 versus 0-85), making 
differences appear more pronounced in the P-index. For example, in cohort B, 
calculating degree of change from right to left, we  nd:
B5 B4 B3 B2 B1
P-Index 0 0.51 1.06 5.26 0.79
H-Index 0 0.55 1.19 2.84 0.65
While P-Index measures a greater change between B3 and B2 than H-Index does,  
there is an overall harmony. The causes behind the B3 to B2 difference are unclear, 
but probably relate to different data sets used to generate the metrics.
Does bibliometrical analysis have an age bias? 
Simple volume plays a signi cant role in driving P-index and H-index values. More 
publications mean higher scores and, as one would expect, senior faculty tend to have 
more publications than younger faculty. However, that effect is less pronounced for 
those over 40 years old. 
Moreover volume alone is not a guarantee of higher P-index and H-index scores. 
Compare D1 with D2 and B1 with B2, for example: 
Cohort Member Publications P-Index H-Index
D1 87 195 7
D2 69 389 18
B1 381 1410 46
B2 328 1789 71
Still senior faculty are more likely than younger to publish in high prestige venues 
and may be more likely to be cited by their colleagues. Overall, age does tend to 
correlate with higher bibliometric scores; both volume and citation frequency play 
a part in that effect. 
P-index versus H-index? 
P-index and the H-index calculations are ultimately grounded in citation analysis, 
but H-index is calculated directly while P-index is calculated obliquely (via ISI 
Impact Factors). If both measurements count the same things in similar ways, why 
choose one over the other?  The most signi cant advantage of the P-index is that its 
calculation can be readily scaled over large numbers of faculty or academic/clinical 
departments. A recent project which entailed generation of P-index values for 1,887 
faculty and 30 academic departments for 3 separate years (5,751 calculations total) 
required less than 25 minutes to complete. H-Index calculation, on the other hand, 
requires by citation by citation comparison. Even with good enabling software, 
H-index is dif cult to scale for large projects. H-Index does have the advantage of 
being more widely used which can make extra-mural comparisons easier.
Publishing and P-Index data for this poster were derived from the NYU School of Medicine 
Faculty Bibliography, an online database curated by the NYU Health Sciences Libraries. 
H-index values were calculated from ISI Web of Knowledge©.


P-Index, A Novel Algorithm for Bibliometric Analysis

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P-Index, A Novel Algorithm for Bibliometric Analysis

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