the culprit for a considerable fraction of overcitation in GS. Whatever the cause, however, this overcitation with 9.5% is much smaller than the undercitation we found for other databases.

The conclusions of our first experi-
ment remain valid, as confirmed in
Figure 2; also, for the editors-in-chief,
there was significant varying RRU for
all types of citations, and the RRU was
particularly large for J2C and C2C cita-
tions. Figure 3 visualizes the h-indexes
and h-cores of the 14 editors-in-chief.
An h-core consists of an author’s x pa-
pers each cited x or more times, with x
being the author’s h-index. 7 The bars
in Figure 3a represent the h-indexes
computed on found citations in WoS,

Figure 3. WoS h-indexes and h-cores for 14 editors-in-chief.

5

10

15

20

5

10

15

20

25

Albers Allender Conte Hoppe Long Özsoyoğlu Renals Lin Nejdl Nuseibeh Ooi Stojmenovic Zabih Zomaya

c
c
c cc
c

c
cc
cc cc
cc

(a) h-index computed on
WoS citation counts
(b) h-index computed on corrected
WoS citation counts

Figure 4. WoS RRus for articles in eight transactions volumes, 2000–2002.

 

J2J C2J

30% 25% 20% 15% 10% 5% 0%

ACM TOCS
ACM TODS
ACM TOG
ACM TOSEM
IEEE TC
IEEE TKDE
IEEE TVCG
IEEE TSE
ACM TOTAL
IEEE TOTAL
TOTAL

Figure 5. underestimation of average journal impact factors, 2002–2003.

J2J only
J2J + C2J

30% 25% 20% 15% 10% 5% 0%

ACM TOCS
ACM TOG
ACM TODS
ACM TOSEM
IEEE TC
IEEE TKDE
IEEE TVCG
IEEE TSE
ACM average
IEEE average

and the bars in Figure 3b represent corrected h-indexes based on relevant citations, confirming h-indexes based on found citations suffer significantly from undercitation. Some authors suffer more than others, to the point their ranking is altered significantly; for example, Ooi was in next-to-last place according to uncorrected WoS citation counts but in third place after correction.

Figures 3a and 3b also show the contribution of conference papers to h-indexes. Each blue/orange box indicates a journal/conference paper in the h-core, ordered left to right from most cited to least cited. For example, Albers has an h-index of 11 in WoS; of the 11 papers in her h-core, the first, fifth, sixth, and 10th most-cited are journal papers. Based on WoS counts, 43% of all papers in the h-cores are conference papers, and based on the corrected counts, 60% are conference papers. Of the five most-cited papers per author, WoS reports 36% are conference papers, whereas the corrected citation counts report 56% are conference papers. These numbers are much higher than those presented by Bar-Ilan1 as obtained from WoS in late 2008/early 2009. This higher count might result from increased coverage in WoS from 2009 to 2011, though we could not verify this conclusion. These results again confirm that using uncorrected WoS citation counts to estimate the importance of conferences for an author can lead to significant underestimation for that author. Moreover, such underestimation varies significantly from author to author; for Zomaya in Figure 2 and Figure 3, WoS attributes 2/12 h-core papers to conferences, which is close to the corrected number of 2/13. However, for Ooi in Figure 2 and Figure 3, WoS attributes 4/11 to conferences, which does not even approximate the corrected number 15/20. We conclude that GS should be used as a complementary source of information to obtain accurate citation counts, even when policy stipulates the citation analysis is limited to WoS coverage. Though this second experiment did not include the ACM DL or Scopus, this conclusion can be extended to those databases, of which the first experiment revealed compa-