Una precisazione sulla scomposizione dell’indice di redistribuzione RE di Aronson-Johnson-Lambert e una proposta di estensione dell’indice di Plotnick

Aronson-Johnson-Lambert redistribution index RE can be correctly applied provided that after taxation incomes maintain the same pre-tax order in what it concerns (i) group average incomes and (ii) within group incomes. If this is not the case, R should be replaced by the transvariation index defined e.g. by Dagum (1997). Of course when R is different from the tranvariation index, in considering RE one neglects income rerankings between groups averages and within groups incomes. This note suggests how information on rerankings may be recovered, through a proper decomposition of Plotnick index. The decomposed Plotnick index might be a useful tool in choosing optimal interval bandwidth, controlling either for group-average reranking and within group reranking.Moreover minor suggestions are added which might be applied in analyzing taxation effects for incomes grouped according to socio-demographic or other criterions.