Google Books Ngram Viewer

Graph these comma-separated phrases:
case-insensitive
between and from the corpus with smoothing of .  
Search in Google Books:

1800 - 1918 1919 - 1971 1972 - 1979 1980 - 1998 1999 - 2008 equality of opportunity English
1800 - 1916 1917 - 1977 1978 - 1984 1985 - 1999 2000 - 2008 equal opportunity English

Run your own experiment! Raw data is available for download here.
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