function gamHat = quartile_coef_skewness(x)
% QUARTILE_COEF_SKEWNESS - returns the quartile coeffient of skewness
%
% Written by:
% -- 
% John L. Weatherwax                2008-02-20
% 
% email: wax@alum.mit.edu
% 
% Please send comments and especially bug reports to the
% above email address.
% 
%-----

% estimate the three quartiles using the "median of the median" method: 
xs    = sort(x); 
q0_5  = median(xs); 
xlt   = xs( find(xs<=q0_5) );
q0_25 = median( xlt ); 
xgt   = xs( find(xs>=q0_5) ); 
q0_75 = median( xgt ); 

gamHat = (q0_75 - 2*q0_5 + q0_25)/(q0_75 - q0_25);