Uncertainty management in the IPCC: agreeing to disagree

Looking back over three and a half Assessment Reports, we see that the Intergovernmental Panel on Climate Change (IPCC) has given increasing attention to the management and reporting of uncertainties, but coordination across working groups (WGs) has remained an issue. We argue that there are good reasons for working groups to use different methods to assess uncertainty, thus it is better that working groups agree to disagree rather than seek to bring everybody on one party line.IPCC; uncertainty

Measurement errors in body size of sea scallops (Placopecten magellanicus) and their effect on stock assessment models

Body-size measurement errors are usually ignored in stock assessments, but may be important when body-size data (e.g., from visual sur veys) are imprecise. We used experiments and models to quantify measurement errors and their effects on assessment models for sea scallops (Placopecten magellanicus). Errors in size data obscured modes from strong year classes and increased frequency and size of the largest and smallest sizes, potentially biasing growth, mortality, and biomass estimates. Modeling techniques for errors in age data proved useful for errors in size data. In terms of a goodness of model fit to the assessment data, it was more important to accommodate variance than bias. Models that accommodated size errors fitted size data substantially better. We recommend experimental quantification of errors along with a modeling approach that accommodates measurement errors because a direct algebraic approach was not robust and because error parameters were diff icult to estimate in our assessment model. The importance of measurement errors depends on many factors and should be evaluated on a case by case basis

Pitfalls of monetary policy under incomplete information: imprecise indicators and real indeterminacy

Can a strategy of targeting macro projections be the only guide for monetary policy actions, or could it cause macroeconomic instability in the face of imprecise information? The paper examines how the precision of the indicators affects determinacy in a model with partial information and an optimizing central bank. When the information on endogenous variables is noisy, the central bank acts too timidly and sunspots arise; relying on information on exogenous variables such as potential output can also induce too much caution in response to inflation. Simple rules which impose a large reaction to nominal variables, irrespective of their information content, may be needed to supply an anchor for prices. Appointing a “conservative” central banker may also be appropriate in presence of large uncertainty, irrespective of time inconsistency considerations, as he responds less timidly to signs of inflation or deflation when their interpretation is difficult.Monetary policy, information variables, incomplete information.

Pitfalls of monetary policy under incomplete information: imprecise indicators and real indeterminacy

The paper examines the link between the precision of the available monetary policy indicators and the determinacy of equilibrium in a forward-looking macroeconomic model with partial information and an optimizing central bank. When the information on endogenous variables is not precise enough, the central bank acts too timidly; there is a possibility of self-fulfilling fluctuations in inflation and output. It is argued that, unless they are very precise, projections of output or inflation over the relevant horizon cannot be the only criterion for determining monetary policy actions. Rules which include a sufficient reaction to nominal variables may be necessary to supply an anchor for prices, even when the policymaker intends to consider all relevant information. Appointing a “conservative” central banker may also induce a less timid response to signs of inflation or deflation, even when their interpretation is difficult. In contrast, relying too much on measures of exogenous variables, such as potential output, can be counter-productive, because it could induce an attitude that is not responsive enough to inflation or deflation.Monetary policy, information variables, incomplete information

QoS routing in ad-hoc networks using GA and multi-objective optimization

Much work has been done on routing in Ad-hoc networks, but the proposed routing solutions only deal with the best effort data traffic. Connections with Quality of Service (QoS) requirements, such as voice channels with delay and bandwidth constraints, are not supported. The QoS routing has been receiving increasingly intensive attention, but searching for the shortest path with many metrics is an NP-complete problem. For this reason, approximated solutions and heuristic algorithms should be developed for multi-path constraints QoS routing. Also, the routing methods should be adaptive, flexible, and intelligent. In this paper, we use Genetic Algorithms (GAs) and multi-objective optimization for QoS routing in Ad-hoc Networks. In order to reduce the search space of GA, we implemented a search space reduction algorithm, which reduces the search space for GAMAN (GA-based routing algorithm for Mobile Ad-hoc Networks) to find a new route. We evaluate the performance of GAMAN by computer simulations and show that GAMAN has better behaviour than GLBR (Genetic Load Balancing Routing).Peer ReviewedPostprint (published version

Aggregate returns to scale: why measurement is imprecise

The extent to which there are aggregate returns to scale at the level of aggregate production has important implications both for the types of shocks generating business cycles and for optimal policy. However, prior attempts to measure the extent of these returns using instrumental variable techniques have yielded quite imprecise estimates. In this article, we show that the production shocks implied by a range of returns to scale that encompasses both large increasing returns and large decreasing returns are almost identical. This makes clear that there is a fundamental reason for the imprecision of prior estimates and casts doubt on our ability to generate more precise estimatesBusiness cycles