Italian sociologist, criminologist, and statistician who posited the theory that every person has a “deep ego” of antisocial, subconscious impulses that represent a throwback to precivilized existence. Accompanying this ego, and attempting to keep its latent delinquency in check, according to his concept, is a “superior ego” formed by man's social interaction. This theory, which he published in 1902, bears some resemblance to the discoveries of psychoanalysis that were being made about the same time.

Niceforo taught criminology in Lausanne (Switzerland), Brussels, and elsewhere and statistics at the universities of Naples and Rome (from 1931). Initially he was influenced by the Italian criminologist Cesare Lombroso (1835–1909), who had theorized the existence of a criminal type, identifiable by certain physical features. Niceforo came to believe, however, that crime could be understood only through a thorough investigation—biological, psychological, and sociological—of the normal human being.

One of the first empirical social scientists in Italy, he applied statistics to the problem of finding regularities in social behaviour. Out of these studies came his theory that persons in all societies exhibit certain constant features, which he called residues, one of which was diversity among individuals. He also discerned in every society the stratification of people into social hierarchies and their collection into a mass, observable especially in religious and national ideological systems.

In elaborating his theory of man's dual ego, he maintained that the deep ego often successfully evades the attempts of the superior ego to control it. This view is detailed in his L' “io” profondo e le sue maschere (1949; “The Deep Ego and Its Masks”).