Citation Thresholds

Updated July 1, 2010 (second bimonthly period of 2010, Jan. 1, 2000-Apr 30, 2010, a 10-year + 4-month period)

Essential Science IndicatorsSM from Thomson Reuters identifies the "essential core" of journal articles, scientists, institutions, countries, and journals from this large data corpus by setting selection criteria (a certain number of citations) for each of the disciplines. These thresholds, set to select some constant fraction of items, are described in an accompanying document (citation thresholds). For example, for highly cited papers, Essential Science Indicators selects the top 1% of articles by total citations in each annual cohort from each of the 22 disciplines. Highly cited papers in Essential Science Indicators total about 90,000 items. Essential Science Indicators also identifies "hot papers," which date from the last two years and which have received an unusually high number of citations during the most recent two-month period. About 1,800 hot papers are selected, representing the top 0.1% in the two-year period.
 
 

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Citation Thresholds for Scientists, Countries, Institutions, and Journals

Essential Science Indicators from Thomson Reuters rankings are based on a selection of the most cited scientists, institutions, countries, and journals in a ten-year period. To compensate for varying citation rates across scientific fields, different thresholds are applied to each field. The thresholds are set to select roughly the same proportion of entities from each field. For scientists the top 1% of names is selected for each of the fields. This percentage of inclusion translates into a specific citation frequency cutoff for each field. For institutions this percentage is also 1%, but for countries and journals 50%.

Field Scientist Country Institution Journal
Agricultural Sciences 236 310 827 556
Biology & Biochemistry 768 435 3862 2806
Chemistry 987 604 3184 2467
Clinical Medicine 1421 2115 1544 2462
Computer Science 154 86 913 434
Economics & Business 238 69 1818 484
Engineering 268 295 862 736
Environment/Ecology 407 587 1771 1416
Geosciences 610 537 2509 800
Immunology 740 518 3692 3417
Materials Science 464 379 1335 811
Mathematics 180 135 1737 769
Microbiology 592 516 3061 2058
Molecular Biology & Genetics 1260 409 6260 3396
Multidisciplinary 160 34 576 82
Neuroscience & Behavior 982 232 3988 4401
Pharmacology & Toxicology 367 266 2114 1563
Physics 2108 765 4740 2317
Plant & Animal Science 403 644 1270 1149
Psychiatry/Psychology 528 113 2100 1328
Social Sciences, general 159 153 525 317
Space Science 2296 181 10525 802


The proportion of top entities selected for each type of entity is given below:

Entity/Percentage Selected:

  • Scientist: 1%
  • Institution: 1%
  • Countries: 50%
  • Journals: 50%

Highly Cited Papers Thresholds

Thresholds are also set to select highly cited papers to be listed in Essential Science Indicators from Thomson Reuters. In this case different thresholds are set for both field and year of data. Setting different thresholds for each year period allows comparable representation for older and younger papers for each field. For each field and time period the top 1% of papers is selected. This table shows the citation count thresholds for each field and year corresponding to this top cut. In the selection process the appropriate threshold is compared against the cumulative citation count for each paper.

Rank 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
Agricultural Sciences 99 87 79 74 61 47 35 25 14 6
Biology & Biochemistry 221 202 185 168 141 110 82 59 35 14
Chemistry 147 134 135 115 106 89 66 50 30 13
Clinical Medicine 190 174 165 149 129 108 81 58 32 12 3
Computer Science 70 73 75 51 38 33 23 21 13 5
Economics & Business 131 103 93 77 62 48 33 23 12 5 3
Engineering 68 64 59 55 48 38 29 22 13 6
Environment/Ecology 148 137 132 111 98 78 58 41 23 9 3
Geosciences 135 118 104 88 77 64 50 33 21 9 4
Immunology 268 266 246 220 189 157 127 93 52 22 4
Materials Science 107 95 91 94 78 66 51 36 22 9
Mathematics 54 47 44 37 33 28 21 15 10 5
Microbiology 192 171 162 141 129 108 82 52 32 13 9
Molecular Biology & Genetics 388 351 309 275 226 194 143 108 65 25 4
Multidisciplinary 67 104 116 119 102 74 79 58 52 22 5
Neuroscience & Behavior 256 248 211 173 146 125 96 64 36 14
Pharmacology & Toxicology 149 156 147 122 108 81 71 48 28 11
Physics 140 131 112 100 90 73 56 40 26 10
Plant & Animal Science 105 101 96 81 74 57 43 31 18 8 3
Psychiatry/Psychology 168 152 134 123 106 76 61 40 21 8 3
Social Sciences, general 75 67 63 55 49 39 28 19 11 5
Space Science 163 178 151 151 132 117 92 69 40 19 3

Hot Papers Thresholds

The selection of Hot Papers in Essential Science Indicators from Thomson Reuters is similarly based on selecting the top cited papers in different fields, but the time frame for citing and cited papers is much shorter, namely, papers must be no more than two years old and cited within a current two-month time period. This means that papers must have received attention within a recent time frame. Papers are assigned to two-month periods and thresholds are set for each period and field to select 0.1% of papers, as shown in this table. The selection process compares the appropriate threshold against the citation count of the paper in the most recent two-month period. Also see "Methodology," for other information on how Essential Science Indicators works.

Rank 2008
-3
2008
-4
2008
-5
2008
-6
2009
-1
2009
-2
2009
-3
2009
-4
2009
-5
2009
-6
2010
-1
2010
-2
Agricultural Sciences 5 6 8 6 6 6 4 7 3 3 2 2
Biology & Biochemistry 13 16 16 13 24 12 11 10 8 5 4 3
Chemistry 15 13 16 10 13 13 10 10 9 5 5 3
Clinical Medicine 15 15 14 13 11 14 12 11 9 8 4 4
Computer Science 6 7 6 9 6 8 8 6 4 3 4 2
Economics & Business 7 7 6 6 6 5 4 5 3 4 2 4
Engineering 7 6 6 6 6 6 6 5 4 3 4 2
Environment/ Ecology 9 9 10 8 8 9 6 7 5 4 3 6
Geosciences 10 9 10 8 7 7 6 7 5 5 4 11
Immunology 28 19 22 18 24 24 16 30 13 10 9 9
Materials Science 9 12 11 9 10 8 9 10 9 6 3 3
Mathematics 5 7 6 7 5 6 4 4 4 3 3 2
Microbiology 14 10 17 10 12 11 8 17 14 5 9 4
Mol. Bio. & Genetics 30 26 28 24 26 19 18 15 16 8 9 12
Multidisciplinary 14 20 18 12 30 15 12 14 15 10 7 4
Neuroscience & Behavior 14 13 12 12 14 16 14 9 7 8 4 4
Pharmacology & Toxicology 10 12 16 10 14 9 7 8 5 4 3 4
Physics 12 9 19 9 11 9 11 10 11 7 6 3
Plant & Animal Science 8 9 7 6 8 7 6 6 5 4 3 8
Psychiatry /Psychology 10 9 9 7 9 7 6 6 5 3 7 6
Social Sciences, general 6 6 4 4 6 5 4 4 3 3 2 7
Space Science 14 18 9 15 66 13 20 10 8 10 5 4
 

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