Search for uni- or bigrams in 96% (n = 27.108) of all songs, excluding instrumentals (n=986) and missing songs (n=279) that appeared on the Billboard Hot 100 from 1956-2016 and see the percentage of songs that contain these grams per year.
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2020 - Article:
Changes in Lyrical and Hit Diversity of Popular U.S. Songs
is not, isn't, ain't