Table 2.
Number of keywords and links by average publication year (APY)
| APY | Number of keywords | Number of links |
|---|---|---|
| 2011 | 207 | 1,825 |
| 2012 | 279 | 4,231 |
| 2013 | 303 | 4,386 |
| 2014 | 203 | 1,233 |
| 2015 | 148 | 620 |
| 2016 | 53 | 66 |
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