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Number of articles published by year and grouped by geographic location.
| Year | Total | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| 1980 | 1985 | 1990 | 1995 | 2000 | 2005 | 2010 | |||
| Continent | North America | 83 | 91 | 102 | 83 | 65 | 112 | 82 | 618 |
| Europe | 3 | 8 | 10 | 12 | 11 | 29 | 34 | 107 | |
| Asia | 3 | 5 | 8 | 2 | 8 | 26 | 22 | 74 | |
| South America | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 1 | |
| Africa | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | |
| Australia/New Zealand | 1 | 1 | 1 | 0 | 3 | 1 | 4 | 11 | |
| Collaborative | 0 | 1 | 0 | 0 | 1 | 4 | 3 | 9 | |
| Total | 91 | 106 | 121 | 97 | 88 | 173 | 145 | 821 |
