摘要
投資人原本預計環球市場將於夏季刷新上升記錄，但漲勢卻被令人憂慮的波動中斷。環球市場經歷自2020年年初疫情爆發以來最劇烈的調整，其中，東證股價指數（TOPIX）在8月份創下近四十年來最大跌幅，而衡量華爾街恐慌情緒的芝加哥期貨交易所波動指數則在出現歷史性波動後靠穩。
8月2日公佈的美國就業數據疲弱可能觸發市場拋售，隨後日本利率意外上升及日圓走強，導致日圓利差交易平倉活動增加，引發市場廣泛不安。今年引領市場上漲的多間大型科技公司在這輪大規模拋售中遭受最大打擊。事實上，在最近的業績期，由於科技行業未能滿足投資人的高預期，這些科技巨擘已出現疲態。以科技股為主的納斯達克指數在7月最後一週下跌3.4%，自7月11日創下歷史新高以來，納斯達克指數截至8月5日收市已下跌逾10%。
市場將繼續劇烈波動
近期發生的多宗事件發出了一個強烈警號，就是資產價格快速升跌及波動激增的情況可能持續，尤其是市場焦點仍然是總體風險﹙例如經濟衰退的可能性及美國經濟數據出乎市場意料﹚以及地緣政治風險。地緣政治風險（包括中東衝突對市場的潛在影響）加劇了市場的不確定性，而即將在11月5日舉行的美國總統大選使不確定性進一步放大。
圖1：波動事件對指數的影響
近期的事件也導致投資人需要加強下檔保護，採用低波動策略可滿足相關需求。
估值過高令人關注
截至2024年6月，市場對未來成長預期的信心高得驚人。從圖2所見，全球十大股票中有五隻估值過高，以至投資人需要公司在不計成本營運的情況下，全數派發銷售收入，並且持續十年以上，才能夠收回成本。如果僅考慮獲利，實現利潤的時間甚至更加遙遠，某些情況下延長至22世紀！
有人認為這些公司的成長能夠支撐估值，但當中多間公司在競爭激烈的週期性行業營運，需要大量研發投資。這些公司的銷售水平已接近或刷新記錄，作為全球規模最大的公司，收入倍增或增加三倍絕非易事。
圖2：以當前收入及獲利計算，MSCI所有國家世界指數十大股票的回本年份
儘管科技行業的估值最為極端，但從圖3所見，其他行業也受到影響，且與過去相比，更多股票的估值高於歷史中位數（紅線），這些股票在指數中的權重也更高。這意味著投資人正支付更高價格，購買佔投資組合比例越來越高的股票。
以20世紀的說法作比喻，他們在爵士樂時代進行的投資，最快要到搖滾樂時代才能兌現報酬，有時更要到Disco、Grunge，甚至Taylor Swift時代初期才能兌現報酬！
即使如此，投資人還需要兩件極不尋常的事情發生才能收回投資︰
從圖2可見，第一個假設不成立，十大股票中，沒有一隻股票將所有獲利作為報酬派發，只有一隻股票將一半以上獲利作為股息派發，意味著投資人只能依賴第二個假設。雖然投資人的確可以出售股票，但正如許多科技股投資人發現，賣出股票時的價格可能低於買入時的價格。
圖3：假設投資人獲得所有獲利的回本年份
被動型投資策略迅速崛起，加劇估值構成的挑戰。根據市值而非基本面價值購買股票的指數基金及交易所買賣基金（ETF）在過去二十年日益普及。雖然這些策略是低成本的分散投資工具，但其也為市場帶來全新動態。隨著越來越多資金流入這些被動型投資工具，這些基金無差別購買最大型公司的股票，無論其估值或成長前景如何。
此「不計價格買入」的方針加劇了估值過高的問題，尤其是市場上最大型的股票。這一現象促成了自我強化的循環，市值最大的公司僅憑其規模而不斷吸引更多投資，可能使其估值無差別地擴大至超出傳統指標評估為合理的範圍。此趨勢導致市值集中於少數巨型股，進一步扭曲整體市場格局，並可能增加系統性風險。
低波動策略是否應對極端市況的仙丹？
與市值加權策略不同，建構低波動投資組合時依據的是股票的歷史價格穩定性，而非其規模或預期成長潛力。此建構方法本質上引導投資人遠離估值過高及炒作主導的行業，並轉向投資估值較合理及穩定的公司。低波動策略往往集中於當前追求成長的市場中經常被忽略的行業，例如公用事業、必需消費品及醫療保健。這些行業通常提供較穩定的獲利及股息，能夠平衡科技股急升的投機炒作特性。此外，低波動方針本質上迴避市場熱潮，能用於防止往往導致泡沫形成的非理性亢奮。
透過對比MSCI所有國家世界指數（圖2）與所有國家世界最低波動指數（圖4）的十大股票，我們會發現回本年份大幅提前，且個股權重較低，顯示投資組合較為平衡及成本較低。
圖4：MSCI所有國家世界最低波動指數十大持股的回本年份
這次的情況真的例外？
我們能發現金融市場的形勢出現巨變。從藍籌股到高風險科技新創公司，從傳統股債到加密貨幣等另類投資，從著重股息的股票到不惜一切代價追求成長的公司，投資人理解及衡量價值的方式不斷演變。
投資人駕馭此全新格局時，平衡潛在成長的吸引力與現實的實際報酬至關重要。這並非表示人工智慧或減肥創新藥物不是革命性，但正如科網泡沫帶來的教訓，即使對科技變革的看法可能正確，投資人仍可能誤判將會從中受惠的公司或應付出的代價。雖然股市未必會回到由股息主導的過去，但市場很少有僅朝一個方向發展。
鑑於市場的這些扭曲現象，將部分資產轉移到低波動投資策略能為投資人提供有用的替代方案。透過聚焦於價格波動較小的股票，投資人長遠有望獲得更穩定的報酬，減少市場大幅下滑的影響。面對被動型策略無意中放大市場低效的時代，低波動方針提供深思熟慮及著重風險的替代方案，可能更加切合當前複雜的金融市場形勢。
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