We are using the Z scores rather than the raw scores
because,The z-score can portray the area of a crude score in the
dispersion of crude scores.
And the z-score is to make an appropriation with a mean of 0
and standard deviation of 1.
Standard scores main purpose:-
The standard score (all the more generally alluded to as a
z-score) is an extremely helpful measurement since it (an) enables
us to ascertain the likelihood of a score happening inside our
typical dispersion and (b) empowers us to look at two scores that
are from various ordinary circulations.