The base corpus is then annotated with four sentiment categories: positive (positive sentiment is expressed in the sentence), negative (the sentence expresses a negative sentiment), neutral (there is no sentiment in the sentence), and mixed (two sentiments are expressed, it is not possible to find a clear dominant one). The annotations were provided by a team of three semi-expert annotators (Master’s students of Linguistics and Digital Humanities). Sentences were used as the unit of annotation, with an average sentence length of 35.7 tokens, the shortest sentence having four tokens and the longest having 350 tokens. A sentence was used as the annotation unit because sentiment often changes within an article and sometimes even within a sentence.