Efficiency comparison of M-estimates for scale at t-distributions

Using Fisher's information for t-distributions, the absolute asymptotic efficiency of some M-estimates for scale with known location parameter is calculated and graphically illustrated. The compared estimators are the standard deviation S-*, the mean absolute deviation, called mean deviation D-*, the median absolute deviation, called MAD(*), and some M-estimates for scale, one, which is very robust, and another one with high asymptotic efficiency for t-distributions close to the normal. The last one is considered with monotone (in the positive field) and with very late redescending chi-function too. Also the <(sigma)over cap>(*)-arch, an alternative and generalized excess measure defined as the double relative asymptotic variance of the underlying scale estimator <(sigma)over cap>(*) in the previous paper, is calcultated for t-distributions and graphically illustrated, because there is the relation that the higher the asymptotic efficiency of <(sigma)over cap>(*) is, the lower is the corresponding <(sigma)over cap>(*)-arch.