曲奇和牛奶，凱斯·厄本和妮可·基德曼，Jay-Z和碧昂斯，他們都有某種持續的關系。在經濟學領域里，失業和通脹的關系也是這樣。1958年，經濟學家威廉·菲利普斯觀察到一種有趣的現象——失業率下降時，通脹率好像就會上升。這種反向關系后來被稱為菲利普斯曲線。但最近，許多經濟分析師和股票市場觀察人士都在問，美國失業率已經跌破4%，那為什么通脹率還是如此之低（不到2%）呢？

首先，菲利普斯實際上并沒有說失業率下降時通脹率就會上升。在研究了1861-1957年的數據后，他的結論是失業率下降時，工資往往會上升。由于通脹率經常隨之上行，其他經濟學家開始把失業率和通脹率之間的相反關系作為經濟前景的便捷預測指標，并據此推斷央行什么時候會為了抑制通脹而提高利率。出于這樣的原因，現在金融行業已經出現了一些關于菲利普斯曲線為何“不起作用”的討論。

Cookies and milk. Keith and Nicole. Jay-Z and Beyoncé. There are certain relationships that just seem to last. In the world of economics, it’s unemployment and inflation. Way back in 1958, economist William Phillips made an interesting observation. It seemed as though when unemployment went down, inflation went up. The inverse relationship became known as the Phillips Curve, and recently a lot of economic analysts and stock market watchers have been asking, with unemployment below 4%, why is inflation still so low (under 2%)?

First of all, Phillips didn’t actually say when unemployment fell, inflation would go up. After studying data between 1861 and 1957, he made the observation that when unemployment went down, wages tended to rise. Since inflation often goes up after that, other economists started using the inverse relationship between unemployment and inflation as a short hand predictor of what might happen in the economy—and as a clue as to when central banks might raise interest rates in an effort to keep inflation at bay. This has led to some current discussions in the financial industry as to why the Phillips Curve “isn’t working.”

房利美的首席經濟學家道格·鄧肯認為，它沒有“起作用”的原因首先是二者并非因果關系，“菲利普斯曲線描述的是就業和通脹之間的關聯性。二者的關聯程度因時而異，但不會發展成因果關系。”所以，雖然通脹上升有時可能出現在失業率下降的階段，但它們并非一個是因一個是果。

實際上二者之間已經出現過很多次例外情況，它們的反向關系也經常受到質疑。舉例來說，在20世紀70年代，曾經出現過滯漲階段，即失業率和通脹率同時上升。經濟學家米爾頓·弗里德曼甚至說過，失業率和通脹率的反向關系只在短時期內有效。就像布拉德·皮特和安吉麗娜·朱莉的婚姻只維持了兩年。

弗里德曼認為，通脹上升時，工資較低的勞動者可能會突然意識到自己的工資偏低，進而開始要求加薪，或者通過跳槽來提高收入。這就是整體工資水平上升的原因。但這是個短期現象；從長期來看，其他許多因素也會決定通脹是否上升。

嘉信理財的首席投資策略分析師麗茲·安·索德斯指出，目前的決定因素之一就是經濟，其增速一直不足以給工資和通脹帶來壓力，“直到去年中期，名義GDP增長率仍然低于失業率。在歷史上，出現這種情況時，就不會發生菲利普斯曲線所描述的那種關聯。”但她說，去年年中菲利普斯曲線再次開始發揮作用，“我們終于看到平均時薪增速略有提高，只是尚未達到以往周期后半段4%左右的水平。”

It doesn’t “work” because it’s not a cause-and-effect relationship to begin with, according to Doug Duncan, Chief Economist at Fannie Mae. “The Phillips Curve is the observation that there is correlation of employment and inflation. The degree of correlation varies over time. But that does not extend to causation.” So while rising inflation may sometimes occur during times of falling unemployment, one doesn’t cause the other.

In fact, there have been so many exceptions to the inverse relationship, its usefulness is often called into question. For instance, there was the period of stagflation in the 70s when unemployment and inflation both went up. And economist Milton Friedman went so far as to state that the inverse relationship between unemployment and inflation only worked in the short term. Kind of like Brad and Angelina. (Sorry.)

Friedman said that when inflation kicked in, workers who were getting paid lower wages would suddenly realize they were being underpaid and start to ask for raises or change jobs to make more money. That’s why overall wages would go up. But this was a short term phenomenon; over the long term, many other factors would affect whether inflation rose.

Liz Ann Sonders, Chief Investment Strategist at Charles Schwab & Co., points to one determining factor right now as the economy, which hasn’t been growing fast enough to put pressure on wages and inflation. “Up until mid-last year, nominal GDP growth was below the unemployment rate. Historically when that occurs, there has been no Phillips Curve correlation.” But in the middle of last year, she says, the Phillips Curve kicked back in. “We finally saw average hourly earnings kick into a slightly higher gear, albeit not to the 4% or so that historically accompanied the latter part of cycles.”

但這次的工資上漲并未帶動通脹大幅上升。剛剛出爐的CPI報告顯示，今年5月，美國通脹率為0.1%，這讓過去12個月美國CPI降至1.8%的低水平。

鄧肯認為：“勞動者的生產率上升了，因此拿到了更高的工資。這不是通脹。生產率上升的動力來自于企業投資，而且當前環境下往往是對技術工具的投資。”

鑒于菲利普斯曲線描述的關聯具有不確定性而且作用范圍較小，央行無法將其作為可靠的預測工具。就連美聯儲主席杰羅姆·鮑威爾也在6月初講話時提到了菲利普斯曲線，他描述了一個“和目前情況差不多”的低通脹（1.4%）、低失業率（4.1%）階段。鮑威爾說，當時的“宏觀經濟學家對菲利普斯曲線呈平直狀態感到困惑。”他指的是1999年。在那之后的幾年里，互聯網泡沫破裂，大衰退也即將到來。導致大衰退的原因眾多，包括家庭債務、按揭危機以及銀行倒閉。美聯儲政策所要應付的經濟局勢要比通脹和工資之間的簡單關系復雜得多。

在當前經濟中，鮑威爾關注的絕不僅僅是菲利普斯曲線。“用貨幣政策給就業市場施加足夠大的推力從而提高通脹存在讓金融等市場出現不穩定過剩的風險。”換句話說，下調利率來刺激經濟在理論上會帶動工資和通脹上升，但也可能產生反作用。經濟體系中資金過多可能使經濟過熱，而且首先，它形成的局面可能非常類似于引發2008年金融危機的情況。

因此，雖然不能忽視體現失業率和通脹率關系的菲利普斯曲線，但如今的情況要比曲奇和牛奶的簡單關聯更復雜一些。（財富中文網）

譯者：Charlie

審校：夏林

But this time while wages have risen, significant inflation has not followed. The just-released CPI report showed a modest .1% rise in May, pushing inflation at the consumer level down to a rate of just 1.8% over the past 12 months.

“Workers are becoming more productive so businesses are paying them more,” according to Duncan. “This is not inflation. The source of the productivity gain is investment by businesses, often in the current environment in technology tools.”

Given the uncertainty and narrow scope of the Phillips Curve correlations, central banks can’t use the curve as a reliable predictive tool. No less than Fed Chairman Jerome Powell referred to the Phillips Curve in a speech at the beginning of June, describing a period of low inflation (1.4%) and low unemployment (4.1%) that was “not so different from today.” It was a time, he said, that “macroeconomists were puzzling over the flatness of the Phillips Curve.” The year was 1999. In the subsequent years, we saw the collapse of the dot.com boom and the onset of the Great Recession, driven by a myriad of causes, including household debt, the mortgage crisis, and bank failures. Fed policy had to react to economic dynamics infinitely more complicated than the simple relationship between inflation and wages.

In the current economy, Powell has his eye on much more than just the Phillips Curve. “Using monetary policy to push sufficiently hard on labor markets to lift inflation could pose risks of destabilizing excesses in financial markets or elsewhere.” In other words, lowering interest rates in order to stimulate the economy, which theoretically would lead to a growth in wages and inflation, could backfire. Too much money in the system could lead to an overheated economy and a scenario much like the one that led to the 2008 financial crisis in the first place.

So while the Phillips Curve relationship between unemployment and inflation can’t be ignored, today’s equation is a little more complicated than just cookies and milk.