We present a comprehensive study of the masses of pseudoscalar and vector
mesons, as well as octet and decuplet baryons computed in O(a) improved
quenched lattice QCD. Results have been obtained using the non-perturbative
definition of the improvement coefficient c_sw, and also its estimate in
tadpole improved perturbation theory. We investigate effects of improvement on
the incidence of exceptional configurations, mass splittings and the parameter
J. By combining the results obtained using non-perturbative and tadpole
improvement in a simultaneous continuum extrapolation we can compare our
spectral data to experiment. We confirm earlier findings by the CP-PACS
Collaboration that the quenched light hadron spectrum agrees with experiment at
the 10% level.Comment: 36 pages, 7 postscript figures, REVTEX; typo in Table XVIII
corrected; extended discussion of finite-size effects in sections III and
VII; version to appear in Phys. Rev.
