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How Deadly is COVID-19? Understanding the Difficulties with Estimation of its Fatality Rate
To understand how best to combat COVID-19, we must understand how deadly is the disease. There is a substantial debate in the epidemiological literature as to whether the fatality rate is 1% or 0.1% or somewhere in between. In this note, I use an SIR model to examine why it is difficult to estimate the fatality rate from the disease and how long we might have to wait to resolve this question absent a large-scale randomized testing program. I focus on uncertainty over the joint distribution of the fatality rate and the initial number of active cases at the start of the epidemic around January ...
Working Paper
Sophisticated monetary policies
The Ramsey approach to policy analysis finds the best competitive equilibrium given a set of available instruments. This approach is silent about unique implementation, namely designing policies so that the associated competitive equilibrium is unique. This silence is particularly problematic in monetary policy environments where many ways of specifying policy lead to indeterminacy. We show that sophisticated policies which depend on the history of private actions and which can differ on and off the equilibrium path can uniquely implement any desired competitive equilibrium. A large ...
Working Paper
Time-varying risk, interest rates and exchange rates in general equilibrium
Time-varying risk is the primary force driving nominal interest rate differentials on currency-denominated bonds. This finding is an immediate implication of the fact that exchange rates are roughly random walks. We show that a general equilibrium monetary model with an endogenous source of risk variation?a variable degree of asset market segmentation?can produce key features of actual interest rates and exchange rates. The endogenous segmentation arises from a fixed cost for agents to exchange money for assets. As inflation varies, the benefit of asset market participation varies, and that ...
Working Paper
If exchange rates are random walks then almost everything we say about monetary policy is wrong
The key question asked by standard monetary models used for policy analysis is how do changes in short term interest rates affect the economy. All of the standard models imply that such changes in interest rates affect the economy by altering the conditional means of the macroeconomic aggregates and have no effect on the conditional variances of these aggregates. We argue that the data on exchange rates imply nearly the opposite: fluctuations in interest rates are associated with nearly one-for-one changes in conditional variances and nearly no changes in conditional means. In this sense ...
Report
Economic Benefits of COVID-19 Screening Tests
We assess the economic value of screening testing programs as a policy response to the ongoing COVID-19 pandemic. We find that the fiscal, macroeconomic, and health benefits of rapid SARS-CoV-2 screening testing programs far exceed their costs, with the ratio of economic benefits to costs typically in the range of 2-15 (depending on program details), not counting the monetized value of lives saved. Unless the screening test is highly specific, however, the signal value of the screening test alone is low, leading to concerns about adherence. Confirmatory testing increases the net economic ...
Report
Sophisticated monetary policies
In standard approaches to monetary policy, interest rate rules often lead to indeterminacy. Sophisticated policies, which depend on the history of private actions and can differ on and off the equilibrium path, can eliminate indeterminacy and uniquely implement any desired competitive equilibrium. Two types of sophisticated policies illustrate our approach. Both use interest rates as the policy instrument along the equilibrium path. But when agents deviate from that path, the regime switches, in one example to money; in the other, to a hybrid rule. Both lead to unique implementation, while ...
Report
There Is No Excess Volatility Puzzle
We present two valuation models which we use to account for the annual data on price per share and dividends per share for the CRSP Value-Weighted Index from 1929 to 2023. We show that it is a simple matter to account for these data based purely on a model of variation over time in the expected ratio of dividends per share to aggregate consumption under two conditions. First, investors must receive news shocks regarding the expected ratio of dividends per share to aggregate consumption in the long run. Second, the discount rate used to evaluate the impact of this news on the current price per ...
Report
Transitional Dynamics in Aggregate Models of Innovative Investment
What quantitative lessons can we learn from models of endogenous technical change through innovative investments by firms for the impact of changes in the economic environment on the dynamics of aggregate productivity in the short, medium, and long run? We present a unifying model that nests a number of canonical models in the literature and characterize their positive implications for the transitional dynamics of aggregate productivity and their welfare implications in terms of two sufficient statistics. We review the current state of measurement of these two sufficient statistics and ...
Report
The optimal degree of discretion in monetary policy
How much discretion should the monetary authority have in setting its policy? This question is analyzed in an economy with an agreed-upon social welfare function that depends on the randomly fluctuating state of the economy. The monetary authority has private information about that state. In the model, well-designed rules trade off society?s desire to give the monetary authority discretion to react to its private information against society?s need to guard against the time inconsistency problem arising from the temptation to stimulate the economy with unexpected inflation. Although this ...
Report
Time-varying risk, interest rates, and exchange rates in general equilibrium
Under mild assumptions, the data indicate that fluctuations in nominal interest rate differentials across currencies are primarily fluctuations in time-varying risk. This finding is an immediate implication of the fact that exchange rates are roughly random walks. If most fluctuations in interest differentials are thought to be driven by monetary policy, then the data call for a theory which explains how changes in monetary policy change risk. Here we propose such a theory based on a general equilibrium monetary model with an endogenous source of risk variation - a variable degree of asset ...