we can see that Zipf ’s law is quite accurate, in that the value of r.Pr is approximately constant,
and close to 0.1.
The biggest variations are for some of the most frequent words.
In fact, it is generally observed that Zipf ’s law is inaccurate for low and high ranks (high-frequency and low-frequency words).
Table 4.3 gives some examples for lower-frequency words from AP89.