(also called freq/mill in the interface) is a number of occurrences of an item per million tokens, also called i.p.m. (instances per million). It is used to compare frequencies between corpora (or datasets) of different sizes.
Formula
number of hits
: corpus size in millions of tokens
= frequency per million
(an alternative calculation producing the same result)
raw frequency : corpus size in tokens × 1000000 = frequency per million
Relative frequency and text types
The frequency per million is always
related to
the whole corpus or
subcorpus, not to a text type. Restricting the query to one or more text types, using the text type selector or specifying text types in CQL, will affect the number of hits but the frequency per million will still be calculated using the number of tokens in the whole (sub)corpus.
To relate the frequency per million to one or more text types,
create a subcorpus from the text type(s) and restrict the query to this subcorpus.
Example
Looking up the frequency of the word
helps in the British National Corpus (112,181,015 tokens), first in the spoken Text type and then in the spoken subcorpus will produce these results.
| SUBCORPUS SELECTED |
none |
none |
spoken
11,787,138 tokens |
| TEXT TYPE SELECTED |
none |
spoken |
none |
| HITS |
3,116 |
302 |
302 |
| FREQUENCY PER MILLION |
27.75
in relation to the number of tokens in the whole corpus |
2.69
in relation to the number of tokens in the whole corpus |
25.62
in relation to the number of tokens in the subcorpus |
| POSSIBLE INTERPRETATION |
helps appears 27.75 times per million tokens in BNC |
‘spoken’ helps appears 2.69 times per million tokens in BNC |
helps appears 25.62 times per million tokens in the spoken part of BNC |
see also
Statistics in Sketch Engine
Average Reduced Frequency
