NO.PZ2021090804000010
问题如下：
Tom is a very successful entrepreneur. After six years of entrepreneurship, the technology company he founded is now worth $500 million . It is a private company. He is the controlling shareholder and owns 60% of the shares. His only other investment is Apple stock he bought 10 years ago. Apple’s stock price has risen very well over the past decade, which has greatly increased the value of this publicly traded stock position and is now worth $40 million.
Tom recently sought financial advice from Johnson, his private financial advisor. After discussing Tom's personal situation and financial goals, Johnson believes that Tom's current investment portfolio needs to be optimized, and pointed out several important risks and tax-related considerations related to Tom's investment portfolio.
Discuss four important risk and tax-relatedconsiderations that are relevant to Tom’s portfolio.
解释：
Tom’s portfolio consists of two concentrated positions: his ownership share of his technology company and his publicly traded shares in the company of Apple he bought 10 years ago. As such, Tom’s portfolio is not an efficient, diversified portfolio.
Four important risk and tax-related considerations that are relevant to Tom’s portfolio are as follows:
1 The company-specific risk inherent in the concentrated positions
2 The reduction in portfolio efficiency resulting from the lack of diversification
3 The liquidity risk inherent in a privately held
4 The risk of incurring an outsized tax bill that diminishes return if one were to sell part of the concentrated position in an attempt to reduce the other risks
Tom的科技公司是私有的，规模相当小，估值为 5 亿美元。Tom的科技公司等民营企业往往比上市公司小，与大公司相比，可能面临一些不同的风险，包括经营历史更有限或业务组合单一，难以吸引高素质的管理人员等他们获得融资的限制。这些风险，无论是单独还是组合，都使得在私人公司中的集中风险比在公开交易公司中的类似市值的集中风险要高得多。
无论 Tom 的投资是公开交易还是私人持有，集中的头寸都会使投资组合面临更高的风险。 Tom 的投资组合会过度暴露于影响其公司的不利事件风险；因为他的集中头寸使的其资产会承担特定的或非系统性的风险——如果分散化，可以分散风险而得到分散化补偿。因此，Tom 的投资组合由于其头寸集中，很可能是一个效率低下的投资组合。投资组合的风险回报率（夏普比率）低于没有集中头寸时所能达到的水平。
Tom的集中头寸，尤其是其科技公司的股份，也可能面临流动性风险。私人公司的股份不能轻易出售以支付意外开支。流动性的缺乏使剩余投资组合的管理变得复杂。相比之下，由于 Tom购买的苹果公司的股票是上市公司，其股票的流动性风险可能较小，因为它们可以出售——但出售大量头寸可能会产生大量交易成本。
集中头寸的税基通常非常低，有时投资者已持有很长时间。Tom从一开始就拥有他的公司，并在十年前购买了苹果公司的股票，之后价值大幅升值。尽管 Tom 的六年和十年的持有期不是特别长，但自成立以来，这两个资产的价值都显着增长。出售全部或部分这些头寸可能会引发重大的税务责任。
虽然这些和其他考虑因素（特别是Tom可能对公司的情感依恋，毕竟是他财务成功的基础）使简单的出售有问题，但他持有的这两个资产固有的风险可能会超过税收和流动性问题。
集中化的Sharpe ratio高，比分散组合。我不太明白分散化资产额外收益那段，麻烦老师详细解答，谢谢
