S(t) = (number of individuals > t)/n .

But from page 80, chapter 3 of the reference "Lawless, J. F. (2011). Statistical models and methods for lifetime data (Vol. 362). John Wiley & Sons",

esf, S(t) = (number of individuals >= t)/n .

Which formula is correct?

Consider a lifetime data:

t = 9 13 13 18 33 28 31 34

By the definition of esf from the first reference, S(18)= 4/8=0.5.

By the definition of esf from the second reference, S(18)= 5/8=0.625.

Which one is conventional?

Thanks for your attention.