This chapter looks at how the application of error theory and of probability models to social statistics was pursued with growing success in Germany during the last third of the nineteenth century. The most successful and influential of those mathematical writers on statistics was the economist and statistician Wilhelm Lexis. The chapter then studies the index of dispersion that Lexis introduced in 1879. Lexis's writings on dispersion and the distribution of human physical attributes were influential within German anthropometry, which began to make interesting use of the analytical techniques associated with the error law during the last quarter of the nineteenth century. Meanwhile, Francis Edgeworth, the poet of statisticians, was led to probability in the context of his campaign to introduce advanced mathematics into the moral and social sciences. He hoped through analogies to bring the same rigor and elegance to economics and ethics.