This master's thesis addresses the often overlooked aspect of transaction costs, capital injections, and withdrawals in fund management theory. The research collaboration with Havsfonden, a newly launched quantitative ESG investment fund, aims to enhance their understanding of transaction costs and capital injections while improving their investment model. The thesis includes a comprehensive literature review, the development of a portfolio model that integrates transaction costs and capital injections, and the numerical implementation and testing of the model using MATLAB. Three distinct models focusing on transaction costs, including linear, fixed, and a combination of both, were created. Additionally, three models were developed to examine capital injections, with one based on past performance and the others considering a constant inflow of capital. The findings indicate that our models provide reasonable implementation and effectively capture the nature of capital injections and transaction costs. / Den här uppsatsen ämnar belysa dem många gånger försummade områdena – transaktionskostnader och kapitalinjektioner – inom portföljeteorin. Uppsatsen är i samarbete med Havsfonden, en nylanserad kvantitativ ESG fond, och syftar till att utvidga förståelsen för hur transaktionskostnader och kapitalinjektioner beaktas och kan modelleras. Uppsatsen omfattar en litteraturstudie, ett ramverk som integrerar transaktionskostnader och kapitalinjektioner, samt en numerisk implementation i MATLAB. Tre modeller för transaktionskostnader har utvecklats, vilket omfattar linjära och fasta transaktionskostnader samt en kombinerad version. Därutöver har tre modeller för kapitalinjektioner utvecklas, varav en baseras på portföljens tidigare prestation, medan de andra baseras på ett konstant inflöde av kapital. Resultatet tyder på att modellerna har implementerats riktigt och lyckas skildra dem utmärkande attributen av transaktionskostnader och kapitalinjektioner.

Thesis (MSc)--University of Stellenbosch, 2002. / See article for abstract

資本市場之系統性風險加劇時，對於利率變動型人壽保險所持有之區隔資產將出現大幅波動，進而影響保險公司之清償能力，本研究透過建立區隔資產負債表之隨機模型，檢視系統性風險下對於人壽保險業違約風險之變化，並透過敏感度分析找出對違約風險影響最大的因子。 本研究依據利率變動型壽險之現金流量建立公司之資產負債模型，預期建立Heston (1993)模型描述標的資產的隨機波動過程，相較於以往Black-Scholes (1973)模型更能反映真實的市場波動。本研究藉由資產與負債的變化，衡量保險公司違約風險，同時分析影響違約風險之各項因子，包含解約、死亡與資產配置策略之關聯性。本研究結果顯示，宣告利率、評價時間長度及資產配置策略等皆會影響保險公司之違約風險及其破產幅度。 / When systemic risk of capital markets exacerbates, the segment assets that held by interest sensitive life insurance policies will fluctuate widely and affect insurer's solvency. This paper considers the problem of valuating the default risk of the life insurers under systematic risk, by constructing a stochastic model of segment balance sheet. In this paper, we establish insurer's asset-liability model on the basis of interest sensitive life insurance policies' cash flow.In particular, we use Heston(1993) model to simulate stochastic process of assets, which is better reflect market volatility than Black-Scholes(1973) model in reality. And moreover, by means of the variation on asset and liability, this study evaluating the default risk of life insurers and analyze the factors affect default risk, like the correlation between surrender, death and asset allocation. And using the result of sensitivity analysis to determine which factor is more important, like guaranteed rate, time period of valuation and so on.

本文利用模擬最適化（Simulation Optimization）的技術，來找出適合投資人之最佳資產配置。模擬最適化係為一種將決策變數輸入而使其反應變數得到最佳化結果之技術，在本篇中，決策變數為各種投資標的之資產配置，而反應變數則為投資結果之預期報酬與標準差，模擬最適化可視為一種在可行範圍內尋求最佳解之過程。本篇中模擬最適化之方法係採演化策略法，最適化問題則為具放空限制之多期架構。我們亦進一步與各種傳統的投資保險策略比較，包括買入持有策略（Buy-and-Hold）、固定比例策略（Constant Mix）、固定比例投資保險策略（Constant Proportion Portfolio Insurance）及時間不變性投資組合保險策略（Time-Invariant Portfolio Protection），以驗證模擬最適化的有效性，並以多種評估指標來衡量各種策略績效之優劣。 由實證結果發現，利用模擬最適化求解出每月的最適資產配置，雖然造成每期因資金配置比例變動而提高波動性，另一方面卻能大幅的增加報酬率。整體而言，模擬最適化技術的確能夠有效提升投資績效，使得最終財富增加，並且得到較大的夏普指數及每單位風險下較高的報酬。 / This paper applied simulation optimization technique to search for the optimal asset allocation. Simulation optimization is the process of determining the values of the decision variables that optimize the values of the stochastic response variable generated from a simulation model. The decision variables in our case are the allocations of many kinds of assets. The response variable is a function of the expected wealth and the associated risk. The simulation optimization problem can be characterized as a stochastic search over a feasible exploration region. The method we applied is the evolution strategies and the optimization problem is formulated as a multi-period one with short-sale constraints. In order to verify the effectiveness of simulation optimization, we compared the resulting asset allocation with allocations obtaining using traditional portfolio insurance strategies including Buy-and-Hold, Constant Mix, Constant Proportion Portfolio Insurance, and Time-Invariant Portfolio Protection. We also used many indexes to evaluate performance of all kinds of strategies in this paper. Our empirical results indicated that using simulation optimization to search for the best asset allocation resulted in large volatilities, however, it significantly enhanced rate of return. As a whole, applying simulation optimization indeed gets the better performance, increases the final wealth, makes Sharpe Index large, and obtains the higher return under per unit risk.

本研究探討長期投資人在面臨通貨膨脹風險時的最適投資決策。就長期投資者而言，諸如退休金規劃者等，通貨膨脹是無可避免卻又不易被數量化之風險，因為各國僅公布與之相關的消費者物價指數而沒有公布真實通貨膨脹數值，因此我們延伸Campbell和Viceira(2001)及Brennan和Xia(2002)的模型假設，以消費者物價指數的資訊來校正原先假定符合Vasicek模型之通貨膨脹動態過程。本研究之理論背景為：利用貝式過濾方法(Baysian Filtering Method)，將含有雜訊之消費者物價指數，透過後驗分配得出通貨膨脹動態過程。利用帄賭過程(Martingale Method)求解資產之公帄價格。再引進定值相對風險趨避(Constant Relative Risk Aversion，CRRA)的效用函數，求出最適投資組合下之期末累積財富、各期資產配置以及效用值。 / 本研究歸納數值結果如下： 一、投資期間越長，通貨膨脹學習效果越顯著。投資期間達25年以上時，有學習效果之累積財富為無學習效果時兩倍以上，25年為2.36倍；30年為2.18倍。此外，學習效果對投資人效用改善率於長期投資時也較顯著，投資10年效用改善率為35%，而投資30年則高達1289%，呈非線性成長。以上結果顯示：資產在市場上累積越久，受到通膨影響越明顯，更需要以學習方式動態調整資產配置進行通貨膨脹風險管理。 / 二、風險較趨避之投資人，CRRA參數值越大；於最適投資組合下之期末財富較少，因為風險較趨避投資人偏好低波動度資產組合。風險容忍度低之投資人較需要通貨膨脹之學習，否則效用減損過高，例如CRRA參數為1.5之投資人30年後效用減損65%，CRRA參數為4之投資人效用減損達96.5%。以上數據顯示：風險趨避投資人對風險關注程度較高，考慮學習效果時，較能根據目前通貨膨脹調整資產配置。 / This study examines the optimal portfolio selection incorporating inflation risk learning adjustments for a long-term investor. For long-term investors, it is inevitable to face the uncertainty of inflation. On the other hand, quantifying inflation risk needs more effort since the government announced the information on Consumer Price Index (CPI) rather than the real inflation rates. / In order to measure the inflation rate in planning the long-term investment strategies, we extend the works in Campbell and Viceira (2001) and Brennan and Xia (2002) to construct a stochastic process of the inflation rate. The prior distribution of inflation rate process, which is not directly observable, is assumed to follow the diffusion process. Based on the information of CPI, we then employ the optimal linear filtering equations to estimate the posterior distribution of the inflation rate process. Through these mechanisms, the inflation rate process is closer to reality by learning from CPI. We also construct the optimal portfolio strategy through a Martingale formulation based on the wealth constraints. The optimal portfolio strategies are given in closed-form solutions. / Furthermore, the importance of learning about inflation risk is summarized through the numerical results. (1) When the investment interval is longer, the learning effect becomes more significant. If the investment horizon is longer than 25 years, the wealth accumulation under learning will be twice more than that without learning effect, e.g., the wealth accumulation is approximately 2.36, 2.18 folds at the end of 25, 30 years. Utility increase under learning also become larger for long-term investor, e.g., the utility values will improve 35% after considering learning ability on inflation from 10-year interval, improve 1289% from 30 years. / (2)When the CRRA parameter increases, the investor have lower risk tolerance; and their wealth accumulation become less due to the lower volatility portfolio. A conservative investor requires more learning ability given the inflation, otherwise their utility value will be reduced, e.g., the utility values will be reduced 35% when CRRA=1.5 after 30 years’ investment, 96,5% when CRRA=4.

本研究主要分為三個部分：第一個部分探討壽險公司保單組合之最適資產配置；第二個部分探討確定提撥退休金制度下，員工所面臨的資產配置問題；第三個部分則為方法論的比較研究。此外，本文也探討長命風險(longevity risk)等相關議題。本文在Huang與Cairns (2006) 所提出的資產報酬模型下，推導出累積資產價值的期望值以及變異數，並利用套裝軟體的最佳化程式(optimization programming)獲得給定目標函數下的最適投資策略。 在保單組合資產配置之研究方面，我們分別針對保險公司繼續經營的商品以及即將停賣的商品提出合適的資產配置方式。常數資產配置方式(Constant rebalance rule)適合持續經營的商品，變動資產配置方式(Variable rebalance rule)則適合即將停賣的商品。在常數資產配置方式下，我們能夠得到投資組合的效率前緣線。此外，不管是何種資產配置方式，當保單組合的保單到期日較近時，保險公司必須增加其所持有的現金比例。 在確定提撥制下最適資產配置問題的研究方面，本文的結果符合一般退休基金經理人所採取的生命週期型態投資方式。本研究發現在Lee-Carter模型之下，考慮時間加權可以增加模型的預測能力。而在考慮長命風險下，員工必須採取更積極的投資策略。 本文決定資產配置之方法為預期模型(Anticipative model)，其在評價日時即決定未來的決策，不考慮新訊息對決策的影響。考慮新訊息會對決策產生影響的決定資產配置方法為適應模型(Adaptive model)。在第五章的研究裡，我們比較上述兩種決定資產配置方法之差異。研究結果發現，若以期望值與標準差為判斷標準，兩種決定資產配置方法並沒有絕對的優劣關係。而若在每個決策執行的時間點重新使用預期模型來決定新的資產配置策略，則其所對應的投資策略以及投資績效會與適應模型下的策略與投資績效接近。因此，在無法獲得適應模型投資策略封閉解的情況下，預期模型投資策略可以有效的近似適應模型投資策略。 / The purpose of this thesis is to investigate the asset allocation issue of the long-term investors. Our approach is to calculate theoretical formulae of the first two moments of the accumulated fund; we then adopt optimization programming to find a asset allocation strategy that fits the fund management target. Two kinds of investors are explored. The first one is an investment manager who manages a general portfolio of life insurance policies, and the second one is an employee who starts his career life in a DC pension plan. We also survey the longevity risk issue in this thesis. In the study of “optimal asset allocation for a general portfolio of life insurance policies”, two kinds of rebalancing methodologies are examined. For constant rebalance rule, which is applicable to a continuing business line, we find an efficient frontier in the mean-standard deviation plot that occurs with arbitrary policy portfolios. Also, the insurance company should hold more cash to reduce its illiquidity risk for portfolios in which policies will mature at earlier dates. In the study of “optimal asset allocation incorporating longevity risk in defined contribution pension plans”, we confirm the suitability of the lifestyle investment strategy. Investors in a DC pension plan should be more aggressive when he considers the longevity risk. Furthermore, we proposed a time adjustment technique to capture mortality predictions more precisely in this study. The approach of decision making of this thesis is referred to anticipative model, which does not consider the possible feedback from the future information. On the other hand, the approach of decision making that consider the possible feedback from the future information is referred to adaptive model. We further compare the two approached in the study “Comparative efficiency- anticipative model versus adaptive model”. The numerical results show that investors would not prefer the adaptive approach to the anticipative approach in the mean-variance criterion. Moreover, the downside risk is larger when the strategy is decided by adaptive approach. We also find that the strategy and its numerical distribution of anticipative approach can approximate to that of adapted approach if one re-assesses it at every decision date. Thus, the anticipative approach provides a first approximation on looking for the optimal investment strategy of adaptive model.

本研究著重於分析發行大量長年期利率敏感型契約、高財務槓桿比例的人壽保險業中公司經理人之投資決策，發現台灣壽險業亦存在Canner et al.(1997)提出之資產配置迷思，亦即風險性資產中債券與股票之比率於不同壽險公司間有差異，與共同基金分離理論中陳述之風險態度不同之投資人所持有之債券與股票比率應相同不相符。本文嘗試以Sorensen(1999)提出之擬似動態規劃法(Quasi- dynamic Programming)最適化到期之效用函數，試算經理人於股票及不同到期固定收益債券之最適持有比例。且詳細探討不同風險偏好及投資期限對於壽險公司投資組合之影響。將業主權益之最適投資策略加上負債之複製投資組合成為策略性資產配置結果，並將其與目前台灣壽險公司之資產配置做比較。研究結果顯示： 1.以擬似動態規畫法求得之最適投資組合於不同風險態度下皆為長期債券以及股票。當經理人之風險趨避程度增加時，投資於股票之比例會減少、投資於債券之比例會增加。 2.比較台灣壽險公司之債券與股票配置比例與本研究之結果發現，本資公司之風險態度較外資公司積極，本資公司應提高其債券之持有比例。 本研究最後以Bajeux-Besnainou et al. (2001)提出之資產配置迷思解釋說明本資公司與外資公司持有之債券與股票比率之所以不同非因資產配置迷思之存在，本資公司與外資公司於風險性資產中持有之債券與股票比率是相同的，但因風險態度較為趨避之公司，投資於風險性資產比率下降、提高避險部位之配置，導致整體之股票與債券比率增加。 關鍵字：資產負債管理、策略性資產配置、擬似動態規劃法。

Uma grande dificuldade da gestão financeira é conseguir associar métodos quantitativos às formas tradicionais de gestão, em um único arranjo. O estilo tradicional de gestão tende a não crer, na devida medida, que métodos quantitativos sejam capazes de captar toda sua visão e experiência, ao passo que analistas quantitativos tendem a subestimar a importância do enfoque tradicional, gerando flagrante desarmonia e ineficiência na análise de risco. Um modelo que se propõe a diminuir a distância entre essas visões é o modelo Black-Litterman. Mais especificamente, propõe-se a diminuir os problemas enfrentados na aplicação da teoria moderna de carteiras e, em particular, os decorrentes da aplicação do modelo de Markowitz. O modelo de Markowitz constitui a base da teoria de carteiras há mais de meio século, desde a publicação do artigo Portfolio Selection [Mar52], entretanto, apesar do papel de destaque da abordagem média-variância para o meio acadêmico, várias dificuldades aparecem quando se tenta utilizá-lo na prática, e talvez, por esta razão, seu impacto no mundo dos investimentos tem sido bastante limitado. Apesar das desvantagens na utilização do modelo de média-variância de Markowitz, a idéia de maximizar o retorno, para um dado nível de risco é tão atraente para investidores, que a busca por modelos com melhor comportamento continuou e é neste contexto que o modelo Black-Litterman surgiu. Em 1992, Fischer Black e Robert Litterman publicam o artigo Portfolio Optimization [Bla92], fazendo considerações sobre o papel de pouco destaque da alocação quantitativa de ativos, e lançam o modelo conhecido por Black-Litterman. Uma grande diferença entre o modelo Black-Litterman e um modelo média-variância tradicional é que, enquanto o segundo gera pesos em uma carteira a partir de um processo de otimização, o modelo Black-Litterman parte de uma carteira de mercado em equilíbrio de longo prazo (CAPM). Outro ponto de destaque do modelo é ser capaz de fornecer uma maneira clara para que investidores possam expressar suas visões de curto prazo e, mais importante, fornece uma estrutura para combinar de forma consistente a informação do equilíbrio de longo prazo (priori) com a visão do investidor (curto prazo), gerando um conjunto de retornos esperados, a partir do qual os pesos em cada ativo são fornecidos. Para a escolha do método de estimação dos parâmetros, levou-se em consideração o fato de que matrizes de grande dimensão têm um papel importante na avaliação de investimentos, uma vez que o risco de uma carteira é fundamentalmente determinado pela matriz de covariância de seus ativos. Levou-se também em consideração que seria desejável utilizar um modelo flexível ao aumento do número de ativos. Um modelo capaz de cumprir este papel é o GARCH ortogonal, pois este pode gerar matrizes de covariâncias do modelo original a partir de algumas poucas volatilidades univariadas, sendo, portanto, um método computacionalmente bastante simples. De fato, as variâncias e correlações são transformações de duas ou três variâncias de fatores ortogonais obtidas pela estimação GARCH. Os fatores ortogonais são obtidos por componentes principais. A decomposição da variância do sistema em fatores de risco permite quantificar a variabilidade que cada fator de risco traz, o que é de grande relevância, pois o gestor de risco poderá direcionar mais facilmente sua atenção para os fatores mais relevantes. Ressalta-se também que a ideia central da ortogonalização é utilizar um espaço reduzido de componentes. Neste modelo de dimensão reduzida, suficientes fatores de risco serão considerados, assim, os demais movimentos, ou seja, aqueles não capturados por estes fatores, serão considerados ruídos insignificantes para este sistema. Não obstante, a precisão, ao desconsiderar algumas componentes, irá depender de o número de componentes principais ser suficiente para explicar grande parte da variação do sistema. Logo, o método funcionará melhor quando a análise de componentes principais funcionar melhor, ou seja, em estruturas a termo e outros sistemas altamente correlacionados. Cabe mencionar que o GARCH ortogonal continua igualmente útil e viável quando pretende-se gerar matriz de covariâncias de fatores de risco distintos, isto é, tanto dos altamente correlacionados, quanto daqueles pouco correlacionados. Neste caso, basta realizar a análise de componentes principais em grupos correlacionados. Feito isto, obtêm-se as matrizes de covariâncias utilizando a estimação GARCH. Em seguida faz-se a combinação de todas as matrizes de covariâncias, gerando a matriz de covariâncias do sistema original. A estimação GARCH foi escolhida pois esta é capaz de captar os principais fatos estilizados que caracterizam séries temporais financeiras. Entende-se por fatos estilizados padrões estatísticos observados empiricamente, que, acredita-se serem comuns a um grande número de séries temporais. Séries financeiras com suficiente alta frequência (observações intraday e diárias) costumam apresentar tais características. Este modelo foi utilizado para a estimação dos retornos e, com isso, obtivemos todas as estimativas para que, com o modelo B-L, pudéssemos gerar uma carteira ótima em um instante de tempo inicial. Em seguida, faremos previsões, obtendo carteiras para as semanas seguintes. Por fim, mostraremos que a associação do modelo B-L e da estimação GARCH ortogonal pode gerar resultados bastante satisfatórios e, ao mesmo tempo, manter o modelo simples e gerar resultados coerentes com a intuição. Este estudo se dará sobre retornos de títulos de renda fixa, mais especificamente, títulos emitidos pelo Tesouro Nacional no mercado brasileiro. Tanto a escolha do modelo B-L, quanto a escolha por utilizar uma carteira de títulos emitidos pelo Tesouro Nacional tiveram como motivação o objetivo de aproximar ferramentas estatísticas de aplicações em finanças, em particular, títulos públicos federais emitidos em mercado, que têm se tornado cada vez mais familiares aos investidores pessoas físicas, sobretudo através do programa Tesouro Direto. Ao fazê-lo, espera-se que este estudo traga informações úteis tanto para investidores, quanto para gestores de dívida, uma vez que o modelo média-variância presta-se tanto àqueles que adquirem títulos, buscando, portanto, maximizar retorno para um dado nível de risco, quanto para aqueles que emitem títulos, e que, portanto, buscam reduzir seus custos de emissão a níveis prudenciais de risco. / One major challenge to financial management resides in associating traditional management with quantitative methods. Traditional managers tend to be skeptical about the quantitative methods contributions, whereas quantitative analysts tend to disregard the importance of the traditional view, creating clear disharmony and inefficiency in the risk management process. A model that seeks to diminish the distance between these two views is the Black-Litterman model (BLM). More specifically, it comes as a solution to difficulties faced when using modern portfolio in practice, particularly those derived from the usage of the Markowitz model. Although the Markowitz model has constituted the basis of portfolio theory for over half century, since the publication of the article Portfolio Selection [Mar52], its impact on the investment world has been quite limited. The Markowitz model addresses the most central objectives of an investment: maximizing the expected return, for a given level of risk. Even though it has had a standout role in the mean-average approach to academics, several difficulties arise when one attempts to make use of it in practice. Despite the disadvantages of its practical usage, the idea of maximizing the return for a given level of risk is so appealing to investors, that the search for models with better behavior continued, and is in this context that the Black-Litterman model came out. In 1992, Fischer Black and Robert Litterman wrote an article on the Black-Litterman model. One intrinsic difference between the BLM and a traditional mean-average one is that, while the second provides the weights of the assets in a portfolio out of a optimization routine, the BLM has its starting point at the long-run equilibrium market portfolio(CAPM). Another highlighting point of the BLM is the ability to provide one clear structucture that is able to combine the long term equilibrium information with the investors views, providing a set of expected returns, which, together, will be the input to generate the weights on the assets. As far as the estimation process is concerned, and for the purpose of choosing the most appropriate model, it was taken into consideration the fact that the risk of a portfolio is determined by the covariation matrix of its assets and, being so, matrices with large dimensions play an important role in the analysis of investments. Whereas, provided the application under study, it is desirable to have a model that is able to carry out the analysis for a considerable number of assets. For these reasons, the Orthogonal GARCH was selected, once it can generate the matrix of covariation of the original system from just a few univariate volatilities, and for this reason, it is a computationally simple method. The orthogonal factors are obtained with principal components analysis. Decomposing the variance of the system into risk factors is highly important, once it allows the risk manager to focus separately on each relevant source of risk. The main idea behind the orthogonalization consists in working with a reduced dimension of components. In this kind of model, sufficient risk factors are considered, thus, the variability not perceived by the model will be considered insigficant noise to the system. Nevertheless, the precision, when not using all the components, will depend on the number of components be sufficient to explain the major part of the variability. Moreover, the model will provide reasonable results depending on principal component analysis performing properly as well, what will be more likely to happen, in highly correlated systems. It is worthy of note that the Orthogonal GARCH is equally useful and feasible when one intends to analyse a portfolio consisting of assets across various types of risk, it means, a system which is not highly correlated. It is common to have such a portfolio, with, for instance, currency rates, stocks, fixed income and commodities. In order to make it to perform properly, it is necessary to separate groups with the same kind of risk and then carry out the principal component analysis by group and then merge the covariance matrices, producing the covariance matrix of the original system. To work together with the orthogonalization method, the GARCH model was chosen because it is able to draw the main stylized facts which characterize financial time series. Stylized facts are statistical patterns empirically observed, which are believed to be present in a number of time series. Financial time series which sufficient high frequency (intraday, daily and even weekly) usually present such behavior. For estimating returns purposes, it was used a ARMA model, and together with the covariance matrix estimation, we have all the parameters needed to perform the BLM study, coming out, in the end, with the optimal portfolio in a given initial time. In addition, we will make forecasts with the GARCH model, obtaining optimal portfolio for the following weeks. We will show that the association of the BLM with the Orthogonal GARCH model can generate satisfactory and coherent with intuition results and, at the same time, keeping the model simple. Our application is on fixed income returns, more specifically, returns of bonds issued in the domestic market by the Brazilian National Treasury. The motivation of this work was to put together statistical tolls and finance uses and applications, more specifically those related to the bonds issued by the National Treasuy, which have become more and more popular due to the \"Tesouro Direto\" program. In conclusion, this work aims to bring useful information either for investors or to debt managers, once the mean-variance model can be useful for those who want to maximize return at a given level or risk as for those who issue bonds, and, thus, seek to reduce their issuance costs at prudential levels of risk.

Uma grande dificuldade da gestão financeira é conseguir associar métodos quantitativos às formas tradicionais de gestão, em um único arranjo. O estilo tradicional de gestão tende a não crer, na devida medida, que métodos quantitativos sejam capazes de captar toda sua visão e experiência, ao passo que analistas quantitativos tendem a subestimar a importância do enfoque tradicional, gerando flagrante desarmonia e ineficiência na análise de risco. Um modelo que se propõe a diminuir a distância entre essas visões é o modelo Black-Litterman. Mais especificamente, propõe-se a diminuir os problemas enfrentados na aplicação da teoria moderna de carteiras e, em particular, os decorrentes da aplicação do modelo de Markowitz. O modelo de Markowitz constitui a base da teoria de carteiras há mais de meio século, desde a publicação do artigo Portfolio Selection [Mar52], entretanto, apesar do papel de destaque da abordagem média-variância para o meio acadêmico, várias dificuldades aparecem quando se tenta utilizá-lo na prática, e talvez, por esta razão, seu impacto no mundo dos investimentos tem sido bastante limitado. Apesar das desvantagens na utilização do modelo de média-variância de Markowitz, a idéia de maximizar o retorno, para um dado nível de risco é tão atraente para investidores, que a busca por modelos com melhor comportamento continuou e é neste contexto que o modelo Black-Litterman surgiu. Em 1992, Fischer Black e Robert Litterman publicam o artigo Portfolio Optimization [Bla92], fazendo considerações sobre o papel de pouco destaque da alocação quantitativa de ativos, e lançam o modelo conhecido por Black-Litterman. Uma grande diferença entre o modelo Black-Litterman e um modelo média-variância tradicional é que, enquanto o segundo gera pesos em uma carteira a partir de um processo de otimização, o modelo Black-Litterman parte de uma carteira de mercado em equilíbrio de longo prazo (CAPM). Outro ponto de destaque do modelo é ser capaz de fornecer uma maneira clara para que investidores possam expressar suas visões de curto prazo e, mais importante, fornece uma estrutura para combinar de forma consistente a informação do equilíbrio de longo prazo (priori) com a visão do investidor (curto prazo), gerando um conjunto de retornos esperados, a partir do qual os pesos em cada ativo são fornecidos. Para a escolha do método de estimação dos parâmetros, levou-se em consideração o fato de que matrizes de grande dimensão têm um papel importante na avaliação de investimentos, uma vez que o risco de uma carteira é fundamentalmente determinado pela matriz de covariância de seus ativos. Levou-se também em consideração que seria desejável utilizar um modelo flexível ao aumento do número de ativos. Um modelo capaz de cumprir este papel é o GARCH ortogonal, pois este pode gerar matrizes de covariâncias do modelo original a partir de algumas poucas volatilidades univariadas, sendo, portanto, um método computacionalmente bastante simples. De fato, as variâncias e correlações são transformações de duas ou três variâncias de fatores ortogonais obtidas pela estimação GARCH. Os fatores ortogonais são obtidos por componentes principais. A decomposição da variância do sistema em fatores de risco permite quantificar a variabilidade que cada fator de risco traz, o que é de grande relevância, pois o gestor de risco poderá direcionar mais facilmente sua atenção para os fatores mais relevantes. Ressalta-se também que a ideia central da ortogonalização é utilizar um espaço reduzido de componentes. Neste modelo de dimensão reduzida, suficientes fatores de risco serão considerados, assim, os demais movimentos, ou seja, aqueles não capturados por estes fatores, serão considerados ruídos insignificantes para este sistema. Não obstante, a precisão, ao desconsiderar algumas componentes, irá depender de o número de componentes principais ser suficiente para explicar grande parte da variação do sistema. Logo, o método funcionará melhor quando a análise de componentes principais funcionar melhor, ou seja, em estruturas a termo e outros sistemas altamente correlacionados. Cabe mencionar que o GARCH ortogonal continua igualmente útil e viável quando pretende-se gerar matriz de covariâncias de fatores de risco distintos, isto é, tanto dos altamente correlacionados, quanto daqueles pouco correlacionados. Neste caso, basta realizar a análise de componentes principais em grupos correlacionados. Feito isto, obtêm-se as matrizes de covariâncias utilizando a estimação GARCH. Em seguida faz-se a combinação de todas as matrizes de covariâncias, gerando a matriz de covariâncias do sistema original. A estimação GARCH foi escolhida pois esta é capaz de captar os principais fatos estilizados que caracterizam séries temporais financeiras. Entende-se por fatos estilizados padrões estatísticos observados empiricamente, que, acredita-se serem comuns a um grande número de séries temporais. Séries financeiras com suficiente alta frequência (observações intraday e diárias) costumam apresentar tais características. Este modelo foi utilizado para a estimação dos retornos e, com isso, obtivemos todas as estimativas para que, com o modelo B-L, pudéssemos gerar uma carteira ótima em um instante de tempo inicial. Em seguida, faremos previsões, obtendo carteiras para as semanas seguintes. Por fim, mostraremos que a associação do modelo B-L e da estimação GARCH ortogonal pode gerar resultados bastante satisfatórios e, ao mesmo tempo, manter o modelo simples e gerar resultados coerentes com a intuição. Este estudo se dará sobre retornos de títulos de renda fixa, mais especificamente, títulos emitidos pelo Tesouro Nacional no mercado brasileiro. Tanto a escolha do modelo B-L, quanto a escolha por utilizar uma carteira de títulos emitidos pelo Tesouro Nacional tiveram como motivação o objetivo de aproximar ferramentas estatísticas de aplicações em finanças, em particular, títulos públicos federais emitidos em mercado, que têm se tornado cada vez mais familiares aos investidores pessoas físicas, sobretudo através do programa Tesouro Direto. Ao fazê-lo, espera-se que este estudo traga informações úteis tanto para investidores, quanto para gestores de dívida, uma vez que o modelo média-variância presta-se tanto àqueles que adquirem títulos, buscando, portanto, maximizar retorno para um dado nível de risco, quanto para aqueles que emitem títulos, e que, portanto, buscam reduzir seus custos de emissão a níveis prudenciais de risco. / One major challenge to financial management resides in associating traditional management with quantitative methods. Traditional managers tend to be skeptical about the quantitative methods contributions, whereas quantitative analysts tend to disregard the importance of the traditional view, creating clear disharmony and inefficiency in the risk management process. A model that seeks to diminish the distance between these two views is the Black-Litterman model (BLM). More specifically, it comes as a solution to difficulties faced when using modern portfolio in practice, particularly those derived from the usage of the Markowitz model. Although the Markowitz model has constituted the basis of portfolio theory for over half century, since the publication of the article Portfolio Selection [Mar52], its impact on the investment world has been quite limited. The Markowitz model addresses the most central objectives of an investment: maximizing the expected return, for a given level of risk. Even though it has had a standout role in the mean-average approach to academics, several difficulties arise when one attempts to make use of it in practice. Despite the disadvantages of its practical usage, the idea of maximizing the return for a given level of risk is so appealing to investors, that the search for models with better behavior continued, and is in this context that the Black-Litterman model came out. In 1992, Fischer Black and Robert Litterman wrote an article on the Black-Litterman model. One intrinsic difference between the BLM and a traditional mean-average one is that, while the second provides the weights of the assets in a portfolio out of a optimization routine, the BLM has its starting point at the long-run equilibrium market portfolio(CAPM). Another highlighting point of the BLM is the ability to provide one clear structucture that is able to combine the long term equilibrium information with the investors views, providing a set of expected returns, which, together, will be the input to generate the weights on the assets. As far as the estimation process is concerned, and for the purpose of choosing the most appropriate model, it was taken into consideration the fact that the risk of a portfolio is determined by the covariation matrix of its assets and, being so, matrices with large dimensions play an important role in the analysis of investments. Whereas, provided the application under study, it is desirable to have a model that is able to carry out the analysis for a considerable number of assets. For these reasons, the Orthogonal GARCH was selected, once it can generate the matrix of covariation of the original system from just a few univariate volatilities, and for this reason, it is a computationally simple method. The orthogonal factors are obtained with principal components analysis. Decomposing the variance of the system into risk factors is highly important, once it allows the risk manager to focus separately on each relevant source of risk. The main idea behind the orthogonalization consists in working with a reduced dimension of components. In this kind of model, sufficient risk factors are considered, thus, the variability not perceived by the model will be considered insigficant noise to the system. Nevertheless, the precision, when not using all the components, will depend on the number of components be sufficient to explain the major part of the variability. Moreover, the model will provide reasonable results depending on principal component analysis performing properly as well, what will be more likely to happen, in highly correlated systems. It is worthy of note that the Orthogonal GARCH is equally useful and feasible when one intends to analyse a portfolio consisting of assets across various types of risk, it means, a system which is not highly correlated. It is common to have such a portfolio, with, for instance, currency rates, stocks, fixed income and commodities. In order to make it to perform properly, it is necessary to separate groups with the same kind of risk and then carry out the principal component analysis by group and then merge the covariance matrices, producing the covariance matrix of the original system. To work together with the orthogonalization method, the GARCH model was chosen because it is able to draw the main stylized facts which characterize financial time series. Stylized facts are statistical patterns empirically observed, which are believed to be present in a number of time series. Financial time series which sufficient high frequency (intraday, daily and even weekly) usually present such behavior. For estimating returns purposes, it was used a ARMA model, and together with the covariance matrix estimation, we have all the parameters needed to perform the BLM study, coming out, in the end, with the optimal portfolio in a given initial time. In addition, we will make forecasts with the GARCH model, obtaining optimal portfolio for the following weeks. We will show that the association of the BLM with the Orthogonal GARCH model can generate satisfactory and coherent with intuition results and, at the same time, keeping the model simple. Our application is on fixed income returns, more specifically, returns of bonds issued in the domestic market by the Brazilian National Treasury. The motivation of this work was to put together statistical tolls and finance uses and applications, more specifically those related to the bonds issued by the National Treasuy, which have become more and more popular due to the \"Tesouro Direto\" program. In conclusion, this work aims to bring useful information either for investors or to debt managers, once the mean-variance model can be useful for those who want to maximize return at a given level or risk as for those who issue bonds, and, thus, seek to reduce their issuance costs at prudential levels of risk.

本研究主要是針對投資型年金之資產負債管理作探討，其中是就規避利率風險對於資產負債管理上的影響以及分析資產配置最適化作為研究的架構，而所利用的研究方法乃是取決於建構利率隨機模型並輔以免疫理論與Markowitz投資組合理論，以期在規避利率風險的同時，亦能將資產配置達至最佳化。 首先，為實際模擬出符合現實經濟環境變動下的隨機利率期間模型，本研究利用C.I.R利率期間結構模型來建構年金保單期間的利率結構，並且由於投資型年金之保單價值的累積特性，因此本研究同時亦建構出連接保單價值的投資資產之報酬率型態，進而模擬出各期之現金流量以及各項投資資產的存續期間；再者，藉由Markowitz投資組合理論，以在免疫條件之限制下進行最適資產配置之評估。 最後，以某知名的保險公司所推出的投資型年金商品作為本研究之實證對象，透過模擬之方法，將研究模型中之各項參數予以評估，並且根據上述之研究過程將免疫理論與投資組合理論相連接，以檢視投資型年金商品在規避利率風險的狀態下，其最適之資產配置比例是否與現行法令之規範相牴觸，而能給予適時之建議。另外，由本實證結果可知，經由本研究的分析流程，可以有效地給予年金管理者規劃出年金資產負債管理時的最適投資組合比例，並且在增加外國投資資產時，更能有效的增加年金資產之報酬，同時也不影響保險法對於投資資產的比例與總金額之限制。再者，對於探討規避利率風險前後之資產組合之資產報酬之變化時，可以進一步了解到，當年金管理者在運用免疫策略來規避利率風險時，其所面對的風險成本之多寡，以作為制定避險決策時的依據。 / This research explores the asset-liability management (ALM) for the Investment-Link-Annuity. Two aspects investigated in this research are the interest rate risk and the optimal asset allocation. Moreover, the major issue investigated here is the trade-off between the optimal investment return and the hedge of interest rate risk. We refer this trade-off as ALM cost. By using stochastic interest rate model, Immunization theory and Portfolio Selection Model, we construct an ALM model to achieve the optimal asset allocation given on hedging the interest rate risk under the immunization strategies for the insurance company. First, we utilize the public trading data for investment market in Taiwan and in USA from 1985 to 2000 and the investment-link annuity product of a well-know insurance company in Taiwan to simulate the cash flow and demonstrate the implementation of our model. By analyzing different simulations under various scenarios, the empirical results are as the followings: 1.The ALM cost for immunization strategies is very small, and is estimated to be about 1% to 2%. Therefore, we suggest that insurance companies should start to undertake the asset liability management as soon as possible. 2.If relaxing the investment restrictions of Insurance Law or allowing insurance company to invest in foreign investment market, the overall investment return will be increased and the ALM cost will be reduced effectively.