Esta é para o enriquecimento cultural:
…did you know that Leibenstein attributed his choice of the term ‘X’ for X-efficiency to Tolstoy’s reference in War and Peace: ‘Two armies may be identical in every observable respect – manpower, armaments, cavalry, provisions – yet one army, in possession of an intangible ‘X-factor,’ will soundly defeat the other …’ (Part XIV, II)? In case you like to dig deeper, go on and read Harvey Leibenstein as a Pioneer of Our Time (The Economic Journal). Here (AER) is Leibenstein’s original 1966 article.
Direto do Mahalanobis.