Closed:How to approximate history of SNP by representative selection tests

Question

[vani2lasky99]

I read the article about positive selection. in that article, they approximate the time of the positive selection . in their figure, something wrote like below

 Tajima's D - 250 ky
 |DDAF| - 80 ky
 Fst & XPCLR - 50~70 ky
 |iHS| & XPEHH - 30 ky 
(ky - 1000 years)

How can approximate time of the positive selection by the result of selection tests? I can't understand...