I want to count the occurrences of the English “wanna” structure diachronically, in order to create a frequency per century chart.
My first step was to use the Corpus of Historical American English (COHA). I found 210 occurrences in the 19th century and 1590 in the 20th century. However, I also want to count the data from the 21th century and for that I need to use another corpus, since COHA doesn’t have data from this century.
Fine, so I went to another corpus (a synchronic one) and found 1274 occurrences. The result is shown in the picture.
My problem is: how can I quantify this data correctly? I am only getting more results in the 20th century because of the size of the corpus (COHA has 400 million words and the synchronic current corpus has only 2 billion). Is there any math calculation I may use in order to make such frequency index correct?