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Contents of PMS, Vol. 4, Fasc. 2,
pages 221 - 236
 

TWO APPROACHES TO CONSTRUCTING SIMULTANEOUS CONFIDENCE BOUNDS FOR QUANTILES

M. Csörgő
P. Révész

Abstract: Given some regularity conditions on the distribution function F of a random sample X  ,X  ,...,X  ,
  1  2     n the sequence of quantile processes (n1/2f(Q(y))(Q  (y) -Q(y));0 < y < 1)
              n behaves like a sequence of Brownian bridges (B  (y);0 < y < 1),
   n where Q(y) := F -1(y), the inverse of F (.) , and Q  (y) = X
  n      k:n  if (k- l)/n < y < k/n (k = 1,2,..,n) with the order statistics X    < X   < ...< X
  1:n    2:n         n:n  of the above sample. First, a sequence of consistent direct estimators is proposed for the quantile-density function Q'(y) = 1/f(Q(y)). The latter then also enables us to construct simultaneous confidence bounds for an unknown quantile function Q(y). The second approach makes frequently misused heuristic steps like

1- a = P(F (x) - n-1/2c(a) < Fn(x) < F(x)+ n1/2c(a);-  oo  < x <  oo )
              -1/2           -1          -1/2
     = P(y - n   c(a) < Fn(F  (y)) < y+ n    c(a);
                                       F -1(0) < F- 1(y) < F-1(1))
     = P(F -1(y - n-1/2c(a)) < F -1(y) < F- 1(y + n-1/2c(a));0 < y < 1)
          n                           n
precise for large n , where Fn  is the empirical distribution function of the above random sample, and for a  (-  (0,1), c(a) is defined by

P (0<suyp<1 |B(y)|< c(a))= 1 - a
for a Brownian bridge B(.).

2000 AMS Mathematics Subject Classification: Primary: -; Secondary: -;

Key words and phrases: -

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