当这个问题提出后，很多投资者第一反应是他们的表现是反向关系。但这是事实吗？债券价格上涨时股市是否真的下跌？或者债券价格下跌时股市是否真的上涨？
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由于美联储最近将重新开始其宽松的货币政策以维持经济增长，近期也可能出现这种正相关关系。如果美国30国债收益率继续下降，那么目前股市的上涨趋势可能还会持续。但是，美国30年国债收益率是否可以继续下降？甚至进入负利率时代？通过迈云的Time Series Model 模型显示美国30年期国债利率过去10年的走势（数据源：FRED）。
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Looking at the graph, bond yields indeed seem to be in adownward trend. In the span of less than a year, yields have dropped from 3.46% to 2.11% (as of 12/09/2019). Does this mean that the FRED’s Treasury rates could potentially drop further? If it does, how high can stock prices go?
Several recent trends seem to be pushing yields even lower, such as ECB’s announcement on Thursday to resume quantitative easing and sustained asset purchases by the Fed, which can potentially push yields into negative territory. If we expect a positive correlation between stock and bond prices, we can expect a rallying of the stock market together with the bond prices in the future.
However, an important question investors may ask is: Is such a policy of lowering interest rates sustainable? Can the US T-bond yield turn negative and stay that way? It is not impossible, considering this is already the case for German bonds and shorter-term T-bills. Furthermore, the Fed’s plan to introduce 50- and 100-year bonds will expand the bank’s policy tools, providing further room to push down the yield curve in order to support an expansionary monetary policy.从图中可以看出，美国30年国债收益率似乎确实呈下降趋势。在不到一年的时间内，收益率从3.46％下降到2.11％（截至2009年12月12日）。这是否意味着美国30年国债利率可能会进一步下降？如果是这样，股市价格会涨多远？
最近所有事件发生都似乎推动收益率进一步走低，例如欧洲央行周四宣布恢复量化宽松政策以及美联储将再次开启利率下跌周期，恢复量化宽松政策，这很可能会推动美国30年国债收益率继续下跌。如果我们假设股市和债券价格之间正相关关系成立，那么我们可以预期股市将在未来与债券价格再次一起上涨。
然而，投资者可能会问的一个重要问题是：这种降低利率的政策是否可持续？美国30年国债收益率能否转为负值并保持这种状态？考虑到德国国债和美国短期国库券已经出现这种情况，这并非不可能。此外，美联储计划推出50年期和100年期国债将扩大货币政策工具，为压低收益率曲线提供进一步的空间，以支持扩张性货币政策。
Given the current situation:
What should investor’s expectation of future yields (and hence stock prices) be? Would monetary expansion continue or eventually reverse?
Is the current upward trend in stock prices driven by lowering yields or improving market sentiment? Are we entering a bull market, or would there be a correction if policy intervention ends?
Are current stock prices expensive or cheap? In next week’s article, we would be analysing this question using the Spread AnalysisModel. So stay tuned!
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