享有“債券之王”美譽的比爾·格羅斯認為，股市“目前的定價太過依賴預期”，他的理由是，并不確信美國總統特朗普能推動經濟迅速增長，因為美國的生產率不如以往。

“高增長率及其推動的生產力可能已成遙遠的回憶，一去不返。”格羅斯在本周四上午發布的月度投資展望中如是說。

格羅斯曾因擔任全球共同基金巨頭太平洋投資管理公司（Pimco）的明星債券投資者蜚聲業內，目前擔任駿利資產管理集團基金經理。他時而睿智時而諷刺的月度投資展望廣受歡迎。

本月的投資展望開頭提出一個有點怪異的問題。（格羅斯問：心愛的寵物和一個不認識的人二選一，必須殺死一個，你會怎么選？）

但接下來，他深入剖析現實世界經濟學家和決策者當前面對的難題：近年來經濟增長的一大要素增長停滯不前，原因成謎。

所謂全要素生產率，實際上是指勞動力和資本轉化為產品和服務的效率。對發達經濟體而言，科技、教育、甚至公共衛生領域的進展都包含在全要素生產率中，有時可能體現得并不明顯，但都十分重要。

在關于生產率的爭論中，美國西北大學經濟學家羅伯特·戈登等悲觀人士認定，人們享用電氣化、室內暖通、汽車、噴氣式發動機和互聯網等巨大科技進步“低垂的果實”后，美國經濟的黃金歲月可能已經遠去。而樂觀人士認為，我們無法預見未來的科技進步，有可能科技發展還能繼續推動經濟強勁增長。

本周稍早，美聯儲主席珍妮特·耶倫在密歇根大學的演講也提及這個話題。她當時指出，雖然就業增長強勁，但最近生產率“非常令人失望”。

耶倫說：“經濟增長如此緩慢還能創造如此多就業，顯示問題非常嚴重。說明生產效率增長很慢。”

格羅斯則借助投資展望里的燒腦問題指出，對經濟學家來說，“答案不分對錯。”可在他看來，投資者過于依賴根據歷史表現編制的模型，但用過去預測未來并不一定準確。也正是基于已有估值，股市、高收益債券等資產的價格普遍太高。

格羅斯寫道：“人們對未來的希望太美好，所以股市估值過高，對增長太樂觀，所以高收益債券估值也不低，所有資產價格都炒高了。只有熱愛估值模型，強烈依靠歷史數據做判斷的投資者會相信，今后還會出現過去六年、或者雷曼兄弟倒閉之前幾十年里同樣高額的回報。”（財富中文網）

譯者：Pessy

審稿：夏林

Bill Gross, the so-called “Bond King,” thinks stocks are currently "priced for too much hope," and here's why: He doubts President Trump can deliver rapid economic growth because the United States simply isn’t as productive as it used to be.

“High rates of growth, and the productivity that drives it, are likely distant memories from a bygone era,” he notes in his monthly investment outlook released Thursday morning.

Gross, who rose to prominence as a star bond investor with Pimco, is now a fund manager with Janus, and his sometimes clever, tongue-in-cheek monthly newsletters have a wide following.

This month the newsletter starts with a rather grotesque brainteaser. (Gross asks: “If forced to choose between killing your favorite pet or an anonymous human being, what would you do?”)

But then he dives into the real-life conundrum currently facing economists and policymakers: An important ingredient of economic growth has stalled in recent years, and it’s still a mystery as to why.

Known as total factor productivity, it’s essentially a measure of how efficient workers and capital are in producing services and products. Improvements in technology, education, and even public health can factor into this somewhat ambiguous, but crucial variable for developed economies.

The pessimists in the debate, like Northwestern University economist Robert Gordon, have argued that the best days for the U.S. economy may be behind us, after we already picked the “low hanging fruit” of massive technological improvements like electrification, indoor plumbing, the automobile, jet engines and the Internet. Optimists, meanwhile, argue we cannot foresee the technological improvements of the future, which may still lead to strong economic growth.

Federal Reserve Chairwoman Janet Yellen touched on the debate earlier this week in a speech at the University of Michigan, noting that recently productivity has been “very disappointing,” despite stronger job growth.

“The fact that you can create that many jobs in the context of growth that is so low points to a significant problem,” she said. “And the problem is that productivity growth is very low.”

As with his brainteasers, Gross notes, “There is no right or wrong answer” for economists. But in his view, investors are relying too heavily on models based on history that may not repeat itself. And for this reason, stocks, high-yield bonds, and other asset prices are too high.

“Equity markets are priced for too much hope, high yield bond markets for too much growth, and all asset prices elevated to artificial levels that only a model driven, historically biased investor would believe could lead to returns resembling the past six years, or the decades predating Lehman,” Gross wrote.