Sahm Rule

Sahm Rule: 當失業率的三個月移動平均值從其12個月低點上升至少半個百分點時，它識別出衰退的初始階段。

簡單的法則，不過1970年以來的衰退都被偵測到，而衰退以外並沒有被觸發。本年七月時Sahm Rule已經被觸發，未來幾個月持續被觸發的可能極高（因為去年11、12和本年1月都是失業率低點）。美國將會進入衰退嗎？

看來很準確，但過去準確的法則不代表可以預測未來，始終美國衰退的樣本次數很少，可能屬於overfitting。

Sahm Rule 不考慮失業水平，只看上升趨勢。現在水平其實在低位。而且勞工人數，經濟增長等都不在考慮之中。

根據Dr. Sahm本人說法，創造法則大意是為了盡快刺激/干預經濟去減少衰退對普通家庭的影響。她八月七日的文章：

Even so, there are risks. Recessions have occurred while the labor force is expanding, as in the 1970s, so the current episode would not be a historical outlier for the early stages of recessions. And the hiring rate is now back down to its 2014 levels, when the unemployment rate was 6%. Some of the contributions to the Sahm rule from entrants may also reflect less demand. The layoff rate often rises later in recessions.

Fed Chair Jerome Powell said last week that the data show “an ongoing, gradual normalization of labor market conditions.” And yet the rise in the unemployment rate over the past year, which my rule reflects, now looks like we are past normal and uncomfortably close to recession. It’s time for the Fed to use its own tools and reduce interest rates.

換言之，主要考慮是經濟就業方面，而不是通脹因素。

今晚的非農就業，甚至大選前的就業數據，都會被金融界和商界以這個法則去影響輿論，增加聯儲局降息的壓力。降息很難有懸念。

衰退暫時只是個藉口，重點還是在投資市場。