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ipm
The abbreviations ipm (instances per million) and ppm (parts per million) are measures of relative frequency. They express the average number of occurences of the unit or word in a hypothetical text/corpus with the size of 1 million words.
Eg. The node form běžeckých in the hundred million word corpus SYN2010 occurs 208 times, which is the equivalent of 1,72 ipm, i.e. 1,72 occurences per million words.
Use of ipm/ppm
The main advantage of relativization of frequency based on corpus size enables us to compare numbers from corpora of various sizes. In the case that corpora are not the same size, absolute values can cause confusion. The node form stromek in the corporaSYN2010 and ORAL2008 reaches these values:
| SYN2010 | ORAL2008 | |
|---|---|---|
| Abs. frequency | 440 | 6 |
| Rel. frequency (in ipm) | 3,62 | 4,45 |
Navzdory tomu, o čem vypovídají absolutní frekvence, po přihlédnutí k celkové velikosti korpusů (SYN2010 má 122 mil. pozic, zatímco ORAL2008 jenom 1,35 mil. pozic) je slovo stromek v korpusu ORAL2008 relativně častější.
