Watt, R., & Quinto, J. (2003). Some Simple Graphical Interpretations of the Herfindahl-Hirshman Index and Their Implications (pp. 1-29). Working Document Universidad Autnoma de Madrid and Universidad San Pablo CEU.
http://www.idee.ceu.es/Portals/0/Publicaciones/simple-graphical-interpretations-of-Herfindahl-Hirshman-Index.pdf

has been cited by the following article:

• TITLE: Concentration Risk Indicator

  AUTHORS: Anis Hadzisalihovic, Johann Pruckner, Andreas Kern

  KEYWORDS: Issuer Concentration, Diversification, Rating, Default Probability

  JOURNAL NAME: Journal of Financial Risk Management, Vol.8 No.2, June 20, 2019

  ABSTRACT: In common portfolio theory1, a significant reduction of risk is expected when investments are split into two or more positions. A lower correlation between positions results in a higher risk-reducing portfolio effect. The credit risk of a portfolio is dependent on the default risk of all its issuers. By investing in two different debtors instead of only one, the probability of the total loss is significantly reduced and a debtor concentration is prevented. Concentration risk can be reduced by diversifying the portfolio. How can concentration risk be defined in a quantitative way? The aim of this paper is to determine a key figure, which makes concentration risk measurable.