Null emphasis on the income distribution: the standard mean (a = 1, average income) provides the benchmark point. Weak emphasis on the bottom of the distribution: the geometric mean (a= 0, median income) is empirically generally close to the median. Moderate emphasis on the bottom of the distribution: this case (o.= -3, income of the lower-middle class) is covered mainly to ensure continuity between the median and the low-end of the distribution.