Several shared tasks have addressed negation processing for English: the BioNLP’09
Shared Task 3 (Kim et al. 2009), the i2b2 NLP Challenge (Uzuner et al. 2011), the *SEM
2012 Shared Task (Morante and Blanco 2012), and the ShARe/CLEF eHealth Evaluation
Lab 2014 Task 2 (Mowery et al. 2014).
the tweet corpus has 301 sentences and 59 were annotated as negated (19.60%).