Hierarchical Clustering-Based
Asset Allocation
                                Thomas Raffinot
                                N
T homas R affinot                              obel Pr ize winner Harr y             offset the benefits of diversification (López
is the Head of Quantitative                    Markowitz described diversifi        de Prado [2016b]).
Macro Strategy at Silex-IP
                                               cation, with its ability to enhance         Exploring a new way of capital allo-
in Paris, France.
traffinot@gmail.com                            portfolio returns while reducing      cation, López de Prado [2016a] introduces
                                risk, as the “only free lunch” in investing          a portfolio diversification technique called
                                (Markowitz [1952]). Yet, diversifying a port-        hierarchical risk parity (HRP). One of the
                                folio in real life is easier said than done.         main advantages of HRP is in computing
                                      Investors are aware of the benefits of         a portfolio on an ill-degenerated or even a
                                diversification but form portfolios without          singular covariance matrix. Lau et al. [2017]
                                giving proper consideration to the corre-            apply HRP to different cross-asset universes
                                lations (Goetzmann and Kumar [2008]).                consisting of many tradable risk premia
                                Moreover, modern and complex port-                   indexes and conf irm that HRP delivers
                                folio optimization methods are optimal in            superior risk-adjusted returns. Alipour et al.
                                sample but often provide rather poor out-of-         [2016] propose a quantum-inspired version
                                sample forecast performance. For instance,           of HRP, which outperforms HRP and thus
                                DeMiguel et al. [2009] demonstrate that              other conventional methods.
                                the equal-weighted allocation, which gives                 The starting point of HRP is that a cor-
                                the same importance to each asset, beats the         relation matrix is too complex to be prop-
                                entire set of commonly used portfolio opti-          erly analyzed and understood. If you have
                                mization techniques. In fact, optimized port-                                           1
                                                                                     N assets of interest, there are N ( N − 1)
                                folios depend on expected returns and risks,                                            2
                                but even small estimation errors can result in       pairwise correlations among them and that
                                large deviations from optimal allocations in         number grows quickly. For example, there
                                an optimizer’s result (Michaud [1989]).              are as many as 4,950 correlation coefficients
                                      To overcome this issue, academics              between stocks of the FTSE 100 and 124,750
                                and practitioners have developed risk-based          between stocks of the S&P 500. More impor-
                                portfolio optimization techniques (min-              tantly, correlation matrices lack the notion
                                imum variance, equal-risk contribution, risk         of hierarchy. Actually, Nobel Prize laureate
                                budgeting, etc.) that do not rely on return          Herbert Simon has argued that complex sys-
                                forecasts (Roncalli [2013]). However, these          tems can be arranged in a natural hierarchy
                                still require the inversion of a positive-           comprising nested substructures (Simon
                                definite covariance matrix, which leads to           [1962]). But, a correlation matrix makes no
                                errors of such magnitude that they entirely          differentiation between assets. Yet, some
    Multi-A sset Special Issue 2018                                                       The Journal of Portfolio M anagement    89