Google Books Ngram Viewer

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

1800 - 1901 1902 - 1974 1975 - 1985 1986 - 1997 1998 - 2010 se preocupa de que Spanish
1800 - 1922 1923 - 1965 1966 - 1971 1972 - 2001 2002 - 2010 se preocupa por que Spanish

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