Editing Glottochronology (section)

===Divergence time===
The basic formula of glottochronology proposed by [[Morris Swadesh]] is:

: <math> t = -\frac{\ln(c)}{2\ln(r)}</math>

''t'' = a given period of time from one stage of the language to another (measured in millennia),<ref>{{cite book |last1=McMahon |first1=April |last2=McMahon |first2=Robert |title=Language Classification by Numbers |date=2005 |publisher=OUP Oxford |isbn=9780191535369 |page=180}}</ref> ''c'' = proportion of wordlist items retained at the end of that period and ''r'' = rate of replacement for that word list.

By testing historically verifiable cases in which ''t'' is known by nonlinguistic data (such as the approximate distance from Classical Latin to modern Romance languages), Swadesh arrived at the empirical value of approximately 0.14 for ''L'', (''c''?) which means that the rate of replacement constitutes around 14 words from the 100-wordlist per millennium. This is represented in the table below.

{| class="wikitable"
|+ Glottochronology Time Scale
|-
! Rough Median Dating !! Median Cognate Retention in 100-Word List
|-
| 500 BP || 86%
|-
| 1000 BP || 74%
|-
| 1500 BP || 64%
|-
| 2000 BP || 55%
|-
| 2500 BP || 47%
|-
| 3000 BP || 40%
|-
| 4000 BP || 30%
|-
| 5000 BP || 22%
|-
| 6000 BP || 16%
|-
| 7000 BP || 12%
|-
| 8000 BP || 9%
|-
| 9000 BP || 7%
|-
| 10000 BP || 5%
|}