[Corpora-List] Surprisingly large MI scores

[Brett Reynolds]

"Formulaic language in native speakers: Triangulating  
psycholinguistics, corpus linguistics, and education" by Nick C. Ellis  
and Rita Simpson-Vlach was recently published in _Corpus Linguistics  
and Linguistic Theory_ <http://www.reference-global.com/doi/abs/10.1515/CLLT.2009.003 
 >.

Therein is a table of n-grams in three columns: low, medium, and high  
MI scores. I'm going from memory, but the authors consider roughly  
MI=3 as low, MI=6 as medium, and MI=12 as high.

I have only a very rudimentary understanding of MI scores, but my  
understanding is that an MI of 3 indicates a strong collocation, so I  
wrote to Nick and asked him about it. He wrote back that:

-They used Mike Barlow's Collocate.
-"MI is very sensitive to length of n-gram.

For example, calculating MI for all 2-9 grams in the whole of BNCBaby  
occurring 12+ times, for each N we found the median MI, resulting in:
N Median MI
2 2.234
3 6.723
4 13.085
5 20.835
6 38.925
7 53.612
8 69.046
9 79.962"

I've never seen MI scores of that size. Moreover, when I looked at  
some of the n-grams that appear in the paper using Mark Davies' COCA  
and BNC interfaces, I came up with much lower numbers. Here are some  
examples: the first is the MI in the entire corpus, and the second is  
the MI in the academic subcorpus.

BNC
the content of  2.99 0.34
is one of the 2.41 -0.24
a kind of 4.06 1.41
the extent to which 2.41 -0.24
in other words 4.71 2.05
a great deal of 3.47 0.82

COCA
the content of 3.24 0.90
is one of the 2.66 0.31
a kind of 4.31 1.97
the extent to which 2.66 0.31
in other words 4.83 2.49
a great deal of 3.73 1.38

Again, the numbers in the paper are often four times those above. Can  
anybody help me understand this discrepancy?

Best,
Brett

<http://english-jack.blogspot.com>

-----------------------
Brett Reynolds
English Language Centre
Humber College Institute of Technology and Advanced Learning
Toronto, Ontario, Canada
brett.reynolds at humber.ca




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