Elevated Economic Uncertainty: Causes and Consequences

At “Global Risk, Uncertainty, and Volatility,” a research conference sponsored by the Federal Reserve Board of Governors, Swiss National Bank and the Bank for International Settlements, Zurich, Switzerland (virtual)

在“全球风险、不确定性和波动性”研究会议上，由美联储理事会、瑞士国家银行和国际清算银行主办，瑞士苏黎世（虚拟）

Introduction Thank you for the opportunity to speak with you today.

简介 感谢您今天有机会与您交谈。

I am very much attuned to the important work that you're doing on uncertainty.

我非常赞同您在不确定性方面所做的重要工作。

Indeed, as a monetary policymaker, the subject is rarely far from my mind.

事实上，作为一名货币政策制定者，这个话题常常远离我的脑海。

It's not a new subject, of course.

当然，这不是一个新主题。

John Maynard Keynes and Frank Knight provided book-length treatments of the subject a century ago (Keynes, 1921; Knight, 1921).

约翰·梅纳德·凯恩斯 (John Maynard Keynes) 和弗兰克·奈特 (Frank Knight) 在一个世纪前就该主题提供了长达一本书的论述（Keynes，1921；Knight，1921）。

In addition, in 2003, Alan Greenspan observed, "Uncertainty is not just an important feature of the monetary policy landscape; it is the defining characteristic of that landscape" (Greenspan, 2003).

此外，艾伦·格林斯潘 (Alan Greenspan) 在 2003 年指出，“不确定性不仅是货币政策格局的一个重要特征，而且是货币政策格局的决定性特征”（Greenspan，2003）。

Before I begin, let me remind you that the views I express today are my own and are not necessarily shared by my colleagues in the Federal Reserve System.

在开始之前，请允许我提醒大家，我今天表达的观点仅是我个人的观点，不一定得到美联储同事的认同。

My plan is to talk about recent advances in how to measure uncertainty, what may cause uncertainty, what effect uncertainty may have on economic outcomes, and the conduct of monetary policy in the presence of uncertainty.

我的计划是讨论如何衡量不确定性、可能导致不确定性的因素、不确定性可能对经济结果产生什么影响，以及在存在不确定性的情况下实施货币政策等方面的最新进展。

Defining and measuring uncertainty Uncertainty is not directly observable in the same way inflation and economic output are observable.

定义和衡量不确定性 不确定性不能像通货膨胀和经济产出那样直接观察到。

It is therefore more difficult to measure.

因此更难测量。

To complicate matters further, there are three related concepts that are often used interchangeably: risk, volatility, and uncertainty.

更复杂的是，三个相关概念经常互换使用：风险、波动性和不确定性。

According to Frank Knight, risk describes a situation in which the outcome is unknown, but the probability distribution governing that outcome is known.

根据弗兰克·奈特的说法，风险描述了一种结果未知但控制该结果的概率分布已知的情况。

Volatility, often used synonymously with risk, is a statistical measure of the variation in observed outcomes.

波动性通常与风险同义，是对观察结果变化的统计衡量。

In contrast, uncertainty is characterized by both an unknown outcome and an unknown probability distribution.

相反，不确定性的特点是未知的结果和未知的概率分布。

These concepts are used interchangeably, in part, because empirically it can be difficult to identify them separately, and because they all capture aspects of what policymakers do not know when making decisions.

这些概念可以互换使用，部分原因是根据经验很难单独识别它们，而且它们都捕捉到了政策制定者在决策时不知道的方面。

Therefore, the uncertainty measures I will discuss are a mixture of these three concepts, and a theme for me will be the necessity of monetary policymakers to consider what they don't know in their decisionmaking, an argument often attributed to Friedrich Hayek (1974).

因此，我将讨论的不确定性衡量标准是这三个概念的混合体，对我来说，一个主题是货币政策制定者有必要在决策中考虑他们不知道的事情，这一论点通常被认为是弗里德里希·哈耶克（Friedrich Hayek，1974）的观点。

Notwithstanding the difficulty in measuring uncertainty, economists have developed tools to assess it.

尽管衡量不确定性很困难，但经济学家已经开发出了评估不确定性的工具。

In fact, in the past two decades, there has been tremendous growth in research devoted to the subject.

事实上，在过去的二十年里，致力于这一主题的研究有了巨大的增长。

In my talk today, I will focus on four broad categories of uncertainty measures: text-based, survey-based, econometric-based, and financial market-based measures.

在今天的演讲中，我将重点关注四大类不确定性衡量标准：基于文本的衡量标准、基于调查的衡量标准、基于计量经济学的衡量标准和基于金融市场的衡量标准。

1 There have been advances in all four categories, and there are advantages and disadvantages to each of these measures.

1 所有四个类别都取得了进展，并且每项措施都有优点和缺点。

One example of text-based measures of uncertainty is that by Baker, Bloom, and Davis (2016), who created an uncertainty index based on the number of leading newspaper articles that contain a combination of words related to economic policy uncertainty.

Baker、Bloom 和 Davis（2016）提出的基于文本的不确定性衡量标准的一个例子是，他们根据主要报纸文章的数量创建了一个不确定性指数，这些文章包含与经济政策不确定性相关的单词组合。

They showed that newspaper text-based measures are highly correlated with stock price volatility, and that higher values of these measures are associated with lower investment and employment.

他们表明，基于报纸文本的衡量标准与股价波动高度相关，并且这些衡量标准的较高值与较低的投资和就业相关。

An advantage of these measures is that they are high-frequency, real-time measures that can narrow the type of uncertainty being measured by linking particular words regarding uncertainty to a specific topic, such as inflation or monetary policy.

这些指标的优点在于，它们是高频、实时的指标，可以通过将有关不确定性的特定词语与特定主题（例如通货膨胀或货币政策）联系起来，缩小所测量的不确定性的类型。

A limitation of these measures is that they suffer from dual causality with the economic outcomes we are trying to measure, and therefore it is difficult to use them to ascertain what impact (if any) uncertainty has on economic outcomes.

这些措施的局限性在于，它们与我们试图衡量的经济结果存在双重因果关系，因此很难用它们来确定不确定性对经济结果的影响（如果有的话）。

For example, does stock price volatility cause journalists to worry about uncertainty, or is the uncertainty discussed in newspaper articles causing volatility?

例如，股票价格波动是否会导致记者担心不确定性，或者报纸文章中讨论的不确定性是否会导致波动？

I note, though, that this disadvantage is common to all four broad categories of uncertainty measures to greater or lesser degrees.

不过，我注意到，这一缺点或多或少是所有四大类不确定性衡量标准所共有的。

The second set of uncertainty measures is survey based.

第二组不确定性措施是基于调查的。

These measures use responses to questions by households, businesses, and market participants about their forecasts and how certain they are about those forecasts.

这些衡量标准使用家庭、企业和市场参与者对他们的预测以及他们对这些预测的确定性的问题的回答。

Advantages of survey-based measures are that they are explicit about the segments of society facing uncertainty, and they are relatively precise in pinpointing the horizon over which the uncertainty prevails.

基于调查的措施的优点在于，它们清楚地表明了面临不确定性的社会部分，并且在确定不确定性普遍存在的范围方面相对准确。

Disadvantages are that these measures are not necessarily timely in capturing uncertainty around fast-breaking new events, and, depending on the issue, they may be less representative than those based on the news.

缺点是这些措施不一定能及时捕捉快速发生的新事件的不确定性，而且根据问题的不同，它们的代表性可能不如基于新闻的措施。

The third set of uncertainty measures is econometric based.

第三组不确定性度量是基于计量经济学的。

In general, these calculate how far off econometric model forecasts are from actual values at each point in time.

一般来说，这些计算计量经济模型的预测与每个时间点的实际值的偏差有多大。

Intuitively, when uncertainty increases, it becomes harder to predict economic variables.

直观上，当不确定性增加时，预测经济变量就变得更加困难。

Advantages of these measures are that they are easy to interpret and calculate and are less prone to dual causality associated with the economic outcomes of interest.

这些措施的优点是易于解释和计算，并且不易出现与感兴趣的经济结果相关的双重因果关系。

Disadvantages are that they are sensitive to the choice of the econometric forecasting model used to calculate them, and their timeliness depends on the availability of the data the forecasting model uses.

缺点是它们对用于计算它们的计量经济预测模型的选择很敏感，并且它们的及时性取决于预测模型使用的数据的可用性。

The last set of uncertainty measures is market-based measures, which use financial market prices to estimate either realized volatility or option-implied volatility.

最后一组不确定性指标是基于市场的指标，它使用金融市场价格来估计已实现波动率或期权隐含波动率。

For example, one widely used uncertainty measure is the Chicago Board of Options Exchange's Volatility Index, the VIX, which is calculated using equity index options that measure market participants' expectations for the volatility of the S&P 500 index over the coming 30 days.

例如，芝加哥期权交易所波动率指数 (VIX) 是一种广泛使用的不确定性指标，该指数使用股票指数期权计算，衡量市场参与者对未来 30 天内标准普尔 500 指数波动性的预期。

The advantages and disadvantages of these measures are similar to the text-based measures: They are high-frequency, real-time estimates of market participants' views, but they suffer from dual causality with the economic outcomes we are trying to measure.

这些指标的优点和缺点与基于文本的指标类似：它们是对市场参与者观点的高频、实时估计，但它们与我们试图衡量的经济结果存在双重因果关系。

An additional disadvantage is that it is often difficult to specify the type of uncertainty being measured.

另一个缺点是通常很难指定所测量的不确定性的类型。

Current state of uncertainty Based on the range of measures discussed above, what can we say about the current state of uncertainty?

当前的不确定性状态 根据上述讨论的措施范围，我们对当前的不确定性状态有何看法？

Figure 1 shows three measures of uncertainty.

图 1 显示了三种不确定性度量。

The red line is an econometric-based measure constructed by Federal Reserve Board staff (Londono, Ma, and Wilson, 2023) called U.S. economic uncertainty.

红线是由美联储委员会工作人员制定的基于计量经济学的衡量标准（Londono、Ma 和 Wilson，2023），称为美国经济不确定性。

According to this measure, U.S. economic uncertainty reached an all-time high at the onset of the pandemic, came down slightly after the pandemic, but has remained elevated ever since.

根据这一指标，美国经济不确定性在疫情爆发时达到历史最高水平，疫情过后略有下降，但此后一直保持在较高水平。

Consistent with this measure, policymakers, including Federal Open Market Committee (FOMC) participants and central bankers around the globe, have been emphasizing the elevated level of uncertainty, especially related to inflation, and the challenge this poses for monetary policy.

与这一措施一致的是，包括联邦公开市场委员会（FOMC）参与者和全球央行行长在内的政策制定者一直在强调不确定性的升高，尤其是与通胀相关的不确定性，以及这给货币政策带来的挑战。

Since the onset of the pandemic, most FOMC participants have been indicating in the Summary of Economic Projections that they view uncertainty around their forecast of personal consumption expenditure inflation to be higher than the average level of uncertainty over the past 20 years.

自疫情爆发以来，大多数 FOMC 参与者在经济预测摘要中表示，他们认为个人消费支出通胀预测的不确定性高于过去 20 年的平均不确定性水平。

But we policymakers are not alone in this.

但我们政策制定者并不孤单。

The July 2023 and September 2023 issues of the Federal Reserve Beige Book, which summarizes the commentary on current economic conditions of businesses, repeat the words "uncertain" and "uncertainty" much more than the historical average and with much of the uncertainty associated with inflation.

2023年7月和2023年9月的美联储褐皮书总结了对当前企业经济状况的评论，重复使用“不确定”和“不确定性”一词的次数远多于历史平均水平，并且大部分不确定性与通胀相关。

2

2

In contrast to policymakers and commentary from businesses and the econometric-based U.S. economic uncertainty measure, the other two uncertainty measures in figure 1—the VIX index, the black line, and the news-based economic policy uncertainty measure, the blue line—declined quickly after the onset of the pandemic in 2020 and have remained relatively subdued since then.

与决策者和企业评论以及基于计量经济学的美国经济不确定性指标相比，图 1 中的另外两项不确定性指标——VIX 指数（黑线）和基于新闻的经济政策不确定性指标（蓝线）在 2020 年大流行爆发后迅速下降，此后一直保持相对低迷。

One interpretation of the divergence in the measures is that they are capturing different aspects of uncertainty.

对这些措施差异的一种解释是，它们捕捉到了不确定性的不同方面。

Over the past year or so, the lack of predictability of economic outcomes, as captured by the elevated econometric-based U.S. economic uncertainty measure, did not lead to heightened expectations of near-term equity market volatility by market participants or to a higher frequency of discussions of economic policy uncertainty in the news.

在过去一年左右的时间里，基于计量经济学的美国经济不确定性指标的上升所体现的经济结果缺乏可预测性，并没有导致市场参与者对近期股市波动的预期提高，也没有导致新闻中更频繁地讨论经济政策的不确定性。

This leads me to the next topics I want to discuss—namely, what causes uncertainty to increase, and does it matter that the harder-to-predict outcomes are not correlated, at least for now, with a higher VIX index?

这引出了我想讨论的下一个主题，即是什么导致不确定性增加，以及更难预测的结果至少目前与更高的 VIX 指数不相关有什么关系吗？

What causes uncertainty to increase?

是什么导致不确定性增加？

Figure 2 shows the econometric-based U.S. economic uncertainty measure since 1960, scaled in standard deviations from its mean.

图 2 显示了自 1960 年以来基于计量经济学的美国经济不确定性衡量标准，按其平均值的标准差进行缩放。

The figure illustrates a certainty about uncertainty: Uncertainty tends to increase during recessions, the shaded gray areas in the graph.

该图说明了不确定性的确定性：在经济衰退期间，不确定性往往会增加，即图中的灰色阴影区域。

Economic theory offers four mechanisms through which bad events—such as recessions, oil supply disruptions, terrorist attacks, wars, and pandemics—can increase uncertainty (Bloom, 2014).

经济理论提供了四种机制，不良事件（例如经济衰退、石油供应中断、恐怖袭击、战争和流行病）可能会增加不确定性（Bloom，2014）。

First, it is easier to predict the future when "business as usual" prevails in a growing economy (Orlik and Veldkamp, 2022).

首先，当经济增长中“一切照旧”盛行时，更容易预测未来（Orlik 和 Veldkamp，2022）。

Forecasting is harder during recessions and when bad events hit the economy.

在经济衰退期间以及坏事件冲击经济时，预测会更加困难。

This was especially the case during the pandemic, a once-in-a-century disturbance of worldwide consequence.

在这场百年一遇、影响全球的大流行病期间尤其如此。

Some have even argued that the pandemic has caused structural changes that will make it harder to predict future economic outcomes.

一些人甚至认为，大流行引发了结构性变化，这将使预测未来的经济结果变得更加困难。

Second, when business is good, firms are trading actively, which helps to generate and spread information (Van Nieuwerburgh and Veldkamp 2006; Fajgelbaum, Schaal, and Taschereau-Dumouchel, 2017).

其次，当生意好的时候，企业会积极交易，这有助于产生和传播信息（Van Nieuwerburgh 和 Veldkamp 2006；Fajgelbaum、Schaal 和 Taschereau-Dumouchel，2017）。

Bad events disrupt trading activity and the flow of information, and this lack of information increases uncertainty.

不良事件会扰乱交易活动和信息流动，而信息的缺乏会增加不确定性。

Third, public policy that is unclear, hyperactive, or both may raise uncertainty (Pastor and Veronesi, 2013).

第三，不明确、过度活跃或两者兼而有之的公共政策可能会增加不确定性（Pastor 和 Veronesi，2013）。

Fourth, when business is slow, it is cheap to try new ideas and to divert unused resources to research and development; this dynamic leads to microeconomic uncertainty, which may in turn lead to macroeconomic uncertainty (Bachmann and Moscarini, 2011; D'Erasmo and Moscoso-Boedo, 2011).

第四，当业务发展缓慢时，尝试新想法并将未使用的资源用于研发的成本较低；这种动态导致微观经济的不确定性，进而可能导致宏观经济的不确定性（Bachmann 和 Moscarini，2011；D'Erasmo 和 Moscoso-Boedo，2011）。

Of these four theoretical mechanisms, the first one strikes me as a highly likely explanation for uncertainty remaining high today.

在这四种理论机制中，第一个让我觉得很有可能解释当今不确定性仍然很高的情况。

We are still learning about the effects of pandemic-specific factors on the economy.

我们仍在了解大流行特定因素对经济的影响。

Additionally, heightened geopolitical risks have recently contributed to increased uncertainty.

此外，近期地缘政治风险加剧也导致不确定性增加。

3

3

In figure 3 , I decompose the econometric-based U.S. economic uncertainty measure into three subcomponents to investigate which economic outcomes are harder to predict since the pandemic and after the increase in geopolitical tensions.

在图3中，我将基于计量经济学的美国经济不确定性指标分解为三个子组成部分，以调查自大流行以来和地缘政治紧张局势加剧之后哪些经济结果更难预测。

The subcomponents are inflation indicators, the black line; labor market conditions, the red line; and economic output, the blue line.

子组成部分是通货膨胀指标，即黑线；劳动力市场状况，红线；和经济产出，蓝线。

All three subcomponents rose significantly during the pandemic but have behaved quite differently since 2021, with inflation uncertainty becoming the dominant source of aggregate economic uncertainty, especially since the Russian invasion of Ukraine.

所有三个子组成部分在疫情期间均大幅上涨，但自 2021 年以来表现截然不同，通胀不确定性成为总体经济不确定性的主要来源，特别是自俄罗斯入侵乌克兰以来。

A message one could take from this is that, through the eyes of an econometrician with a rich set of predictors, inflation over the past two years was objectively difficult to predict.

人们可以从中得到的信息是，通过一位拥有丰富预测变量的计量经济学家的眼睛，过去两年的通货膨胀客观上很难预测。

The rise in inflation and inflation uncertainty in the post-COVID era has been a global phenomenon.

后疫情时代通胀和通胀不确定性上升已成为全球现象。

The left panel of slide 7, figure 4.1 , plots an econometric-based foreign economic uncertainty index calculated as the equally weighted average of the measures of 38 foreign countries.

第 7 张幻灯片的左图（图 4.1）绘制了基于计量经济学的外国经济不确定性指数，计算为 38 个外国衡量标准的等加权平均值。

As in the case of the U.S. economic uncertainty index, the foreign index spikes around the Global Financial Crisis and soars around the COVID pandemic, and it has remained quite elevated since, at around 3 standard deviations from its historical mean.

与美国经济不确定性指数一样，外国指数在全球金融危机期间飙升，在新冠疫情期间飙升，此后一直保持在相当高的水平，与历史平均值相差约 3 个标准差。

The right panel of slide 7, figure 4.2, shows the components of foreign economic uncertainty: inflation, the black line; labor, the red line; and output, the blue line.

第 7 张幻灯片的右图（图 4.2）显示了外国经济不确定性的组成部分：通货膨胀，黑线；劳动，红线；和输出，蓝线。

Again, as in the U.S., foreign inflation uncertainty has become the dominant source of economic uncertainty.

与美国一样，外国通胀不确定性再次成为经济不确定性的主要来源。

What effect may uncertainty have on economic outcomes?

不确定性会对经济结果产生什么影响？

Now that I have established that some measures of economic uncertainty are elevated, one may wonder, to what extent does it matter?

既然我已经确定一些衡量经济不确定性的指标有所上升，人们可能会想，这有多重要？

Economic theory offers at least two channels for uncertainty to influence growth negatively.

经济理论至少提供了两种不确定性对增长产生负面影响的渠道。

4 The first channel comes from the "real options" literature and the fact that the option value of waiting to make decisions increases with uncertainty (for example, Bernanke, 1983).

4 第一个渠道来自“实物期权”文献以及等待做出决策的期权价值随着不确定性而增加的事实（例如，Bernanke，1983）。

According to this theory, it is optimal for firms to not invest and to not hire new employees when uncertainty is high.

根据这一理论，当不确定性很高时，企业最好不投资、不雇用新员工。

This lack of investment and hiring in turn exacerbates recessions.

投资和招聘的缺乏反过来又加剧了经济衰退。

The second channel comes from the reaction of financial markets to uncertainty.

第二个渠道来自金融市场对不确定性的反应。

Investors require compensation for higher risk and uncertainty in the form of higher risk premia, which manifests in lower equity prices, and higher borrowing costs.

投资者要求以较高风险溢价的形式补偿较高的风险和不确定性，这表现为较低的股价和较高的借贷成本。

In the presence of financial constraints, these tighter financial conditions will reduce economic growth (for example, Christiano, Motto, and Rostagno, 2014).

在存在金融约束的情况下，这些收紧的金融状况将降低经济增长（例如，Christiano、Motto 和 Rostagno，2014 年）。

In addition, higher uncertainty is often accompanied by higher equity market volatility and illiquidity, which in turn exacerbates uncertainty.

此外，较高的不确定性往往伴随着较高的股市波动性和流动性不足，这反过来又加剧了不确定性。

As I mentioned earlier, the elevated econometric-based uncertainty measure this past year has not been accompanied by higher equity market volatility, as measured by the VIX index.

正如我之前提到的，过去一年基于计量经济学的不确定性指标的上升并没有伴随着以 VIX 指数衡量的股市波动性的上升。

This suggests that the economic effects of the higher economic uncertainty may be somewhat mitigated, relative to the more serious case where higher economic uncertainty is accompanied by a higher VIX index (Ludvigson, Ma, and Ng, 2021).

这表明，相对于较高的经济不确定性伴随着较高的 VIX 指数的更严重的情况，较高的经济不确定性的经济影响可能会有所减轻（Ludvigson、Ma 和 Ng，2021）。

Because uncertainty can influence growth negatively, policymakers often aim to reduce uncertainty about their objectives.

由于不确定性会对增长产生负面影响，政策制定者往往致力于减少其目标的不确定性。

One way they attempt to do this is by adopting a systematic approach to achieving their objectives, as circumstances allow.

他们尝试做到这一点的一种方法是在情况允许的情况下采用系统方法来实现其目标。

This point leads me to my final topic, the conduct of monetary policy in the presence of uncertainty.

这一点引出了我的最后一个主题，即存在不确定性的情况下货币政策的实施。

What should policy makers do when uncertainty is high?

当不确定性很高时，政策制定者应该做什么？

In 1967, William Brainard argued that uncertainty about the power of monetary policy implied that policy should respond more cautiously to shocks than would be the case if this uncertainty did not exist (Brainard, 1967).

1967 年，威廉·布雷纳德 (William Brainard) 认为，货币政策力量的不确定性意味着政策应对冲击的反应应该比这种不确定性不存在的情况更加谨慎 (Brainard, 1967)。

Brainard's attenuation principle is a classic example of what has come to be known as the Bayesian approach to uncertainty and is often cited as the foundation for gradualism in the adjustment of monetary policy: Calculate what you think your best policy response is for the economy you observe—and then do less.

布雷纳德的衰减原理是所谓的贝叶斯不确定性方法的典型例子，经常被认为是货币政策调整渐进主义的基础：计算你认为对你所观察到的经济体的最佳政策反应，然后减少行动。

It is often suggested, however, that the ambiguity aversion approach to uncertainty leads to anti-attenuation .

然而，人们经常认为，对不确定性的模糊厌恶方法会导致反衰减。

That is, in the face of uncertainty over which a policymaker is unwilling or unable to attach prior probabilities, the appropriate response is to apply stronger monetary medicine than in the certainty equivalence case.

也就是说，面对政策制定者不愿意或无法附加先验概率的不确定性，适当的反应是采用比确定性等价情况更强有力的货币药物。

For example, as Chair Powell mentioned in a speech in 2018 that, during crisis periods, words like "we will do whatever it takes" will likely be more effective than "we will take cautious steps" (Powell, 2018).

例如，正如鲍威尔主席在 2018 年的一次演讲中提到的，在危机时期，“我们将不惜一切代价”之类的话语可能比“我们将采取谨慎的步骤”更有效（Powell，2018）。

Advocates for both approaches have their theoretical justifications.

这两种方法的倡导者都有其理论依据。

In practice, however, the best response to uncertainty can be context specific and can vary over time.

然而，在实践中，对不确定性的最佳反应可能是针对具体情况的，并且可能会随着时间的推移而变化。

5 Fortunately, sometimes the context leads to the same conclusion, broadly speaking, regardless of the approach.

5 幸运的是，有时，无论采用何种方法，从广义上讲，上下文都会得出相同的结论。

One case of perennial interest to central bankers is inflation persistence where both the Bayesian and ambiguity aversion approaches tend to lead to policy that is stronger than the certainty equivalent case to forestall the possibility of inflationary forces becoming embedded in inflation expectations.

中央银行家长期感兴趣的一个例子是通货膨胀的持续性，贝叶斯方法和模糊厌恶方法往往会导致比确定性等效情况更强的政策，以防止通货膨胀力量嵌入通货膨胀预期的可能性。

6

6

Conclusions Let me end where I began.

结论 让我从开始的地方结束。

Monetary policymakers need to consider what they don't know in their decisionmaking, along with what they do know.

货币政策制定者需要在决策时考虑他们所不知道的事情以及他们所知道的事情。

This is not a new idea.

这并不是一个新想法。

We have long appreciated that policy decisions under uncertainty should consider a range of possible scenarios about the state, and the structure, of the economy.

我们长期以来一直认识到，不确定性下的政策决策应考虑一系列有关经济状况和结构的可能情景。

Economic history and recent research have sharpened some of the questions, even if they have not produced the easy policy narratives we might prefer.

经济史和最近的研究使一些问题变得尖锐，即使它们没有产生我们可能喜欢的简单的政策叙述。

What is clear is that policy decisions taken under uncertainty may look quite different from those that would be optimal under certainty, and properly so.

显而易见的是，在不确定性下采取的政策决策可能看起来与在确定性下采取的最优政策决策有很大不同，而且确实如此。

The fact that economic agents are uncertain about their environment and must learn about the economy—and policy—means that monetary policy can be a positive force in stabilizing expectations.

经济主体对其环境不确定，必须了解经济和政策，这一事实意味着货币政策可以成为稳定预期的积极力量。

In my thinking, this prospect serves as a reason for central banks to strive for predictability and transparency in policy actions and communications while avoiding the hubris of overrepresenting the state of our knowledge.

在我看来，这种前景是央行努力实现政策行动和沟通的可预测性和透明度，同时避免过度反映我们的知识状况的傲慢态度的原因。

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1.

1.

For a detailed description of these four categories of uncertainty measures, please see Cascaldi-Garcia and others (2023).

有关这四类不确定性度量的详细描述，请参阅 Cascaldi-Garcia 等人 (2023)。

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2.

2.

The historical average is computed over the sample period from 1996 to the present.

历史平均值是从 1996 年至今的样本期间计算的。

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3.

3.

See, for example, Caldara and Iacoviello (2022) for a measure of geopolitical risk.

例如，请参阅 Caldara 和 Iacoviello (2022)，了解地缘政治风险的衡量标准。

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4.

4.

Economic theory also offers at least two channels for uncertainty to influence growth positively.

经济理论还提供了至少两种不确定性对增长产生积极影响的渠道。

The "growth options" theory argues that uncertainty can encourage investment if it increases the potential prize (Bar-Ilan and Strange, 1996).

“增长选择”理论认为，如果不确定性增加潜在回报，则可以鼓励投资（Bar-Ilan 和 Strange，1996）。

The "Oi-Hartman-Abel" theory after Oi (1961), Hartman (1972), and Abel (1983), argues that if firms can expand to exploit good outcomes and contract to insure against bad outcomes, they may be risk loving.

继 Oi（1961）、Hartman（1972）和 Abel（1983）之后的“Oi-Hartman-Abel”理论认为，如果企业能够扩张以利用良好的结果，并通过收缩来确保避免不良结果，那么它们可能是风险偏好者。

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5.

5.

See Barlevy (2011) for an accessible survey and Tetlow and von zur Muehlen (2001) for a more technical treatment.

参见 Barlevy (2011) 的一项易于理解的调查，以及 Tetlow 和 von zur Muehlen (2001) 的更技术性处理。

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6.

6.

Bernanke (2007) and Powell (2018) highlight this case.

Bernanke (2007) 和 Powell (2018) 强调了这一案例。

Söderstöm (2002) establishes the result for the Bayesian case.

Söderstöm (2002) 确定了贝叶斯案例的结果。

Tetlow (2019) is a simple demonstration of that case alongside the ambiguity aversion case.

Tetlow（2019）是该案例与歧义厌恶案例的简单演示。

Adam and Woodford (2012) show that uncertainty regarding the data generating process for inflation in the New Keynesian model retains as the optimal policy the same general form as in the standard model but with a more aggressive response to inflation.

Adam 和 Woodford（2012）表明，新凯恩斯主义模型中通货膨胀数据生成过程的不确定性保留了与标准模型相同的一般形式作为最优政策，但对通货膨胀的反应更加积极。

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*On November 14, 2023, a revised version of Figure 1 was posted.

*2023年11月14日，发布了图1的修订版本。

The date range of the x-axis was changed from 2019 through 2024 to 2018 through 2023.

x 轴的日期范围从 2019 年至 2024 年更改为 2018 年至 2023 年。