Simple Rules Of Thumb Research Articles

The development of an inherent safety approach to the prevention of domino accidents

The severity of industrial accidents in which a domino effect takes place is well known in the chemical and process industry. The application of an inherent safety approach for the prevention of escalation events leading to domino accidents was explored in the present study. Reference primary scenarios were analyzed and escalation vectors were defined. Inherent safety distances were defined and proposed as a metric to express the intensity of the escalation vectors. Simple rules of thumb were presented for a preliminary screening of these distances. Swift reference indices for layout screening with respect to escalation hazard were also defined. Two case studies derived from existing layouts of oil refineries were selected to understand the potentialities coming from the application in the methodology. The results evidenced that the approach allows a first comparative assessment of the actual domino hazard in a layout, and the identification of critical primary units with respect to escalation events. The methodology developed also represents a useful screening tool to identify were to dedicate major efforts in the design of add-on measures, optimizing conventional passive and active measures for the prevention of severe domino accidents.

Subpopulation Triage: How to Allocate Conservation Effort among Populations

Threatened species often exist in a small number of isolated subpopulations. Given limitations on conservation spending, managers must choose from strategies that range from managing just one subpopulation and risking all other subpopulations to managing all subpopulations equally and poorly, thereby risking the loss of all subpopulations. We took an economic approach to this problem in an effort to discover a simple rule of thumb for optimally allocating conservation effort among subpopulations. This rule was derived by maximizing the expected number of extant subpopulations remaining given n subpopulations are actually managed. We also derived a spatiotemporally optimized strategy through stochastic dynamic programming. The rule of thumb suggested that more subpopulations should be managed if the budget increases or if the cost of reducing local extinction probabilities decreases. The rule performed well against the exact optimal strategy that was the result of the stochastic dynamic program and much better than other simple strategies (e.g., always manage one extant subpopulation or half of the remaining subpopulation). We applied our approach to the allocation of funds in 2 contrasting case studies: reduction of poaching of Sumatran tigers (Panthera tigris sumatrae) and habitat acquisition for San Joaquin kit foxes (Vulpes macrotis mutica). For our estimated annual budget for Sumatran tiger management, the mean time to extinction was about 32 years. For our estimated annual management budget for kit foxes in the San Joaquin Valley, the mean time to extinction was approximately 24 years. Our framework allows managers to deal with the important question of how to allocate scarce conservation resources among subpopulations of any threatened species.

FX-Adjusted Local Currency Spreads

Changes in domestic and international economic conditions affect partly the trend and volatility of the exchange rate as well as the operating conditions of firms and corporations. Therefore, the common practice of adding up the default risk and currency risk premia could overstate the risk compensation received by investors. Modern approaches to model default risk that incorporate foreign exchange effects while promising may be difficult to implement due to data limitations. This paper addresses the needs of practitioners by presenting a simple rule of thumb, based on the joint dynamics of exchange rate changes and the spreads of credit default swaps, to convert foreign-currency denominated spreads to local currency-denominated spreads adjusting for currency risk. The rule of thumb, while simple, captures the nonlinear dependence between default risk and currency risk, and could be very useful for investors in local currency instruments.

Analysis of Worst-Case Fiber Splice Loss Associated with Mechanical Tolerance

An analysis is presented of optical fiber splice loss associated with mechanical tolerance for coated and uncoated avionic fibers coupled in a loose sleeve (glass capillary). A simple prescription is provided for calculating worst-case loss, combining simultaneous contributions from core offset, core diameter mismatch, numerical aperture mismatch, and core ellipticity. Worst-case values are interpreted with the aid of a Monte Carlo analysis, simulating 10,000 splices. The analysis produces a simple rule of thumb relating the worst-case splice loss to the value exceeded by 1% of the simulated splices: “divide the worst-case loss by 3 to get the 1% value.”

Retirement Savings Portfolio Management

We assess the welfare implications of alternative retirement plan investment options given that households may not invest according to optimal portfolio choice theory but may instead use simple decision rules. We simulate the performance of lifestyle, lifecycle, and other simple strategies for allocating retirement savings. We find that if investors use simple rules of thumb to choose investments, then the impact of these strategies on welfare depend to a large extent on the choice set they are offered. If larger choice sets cause them to undertake more risk, then risk tolerant individuals may tend to be made better off. If larger choice sets cause them to reduce suboptimally low levels of portfolio risk, then the increased choice set may make them substantially worse off. The welfare effects of plan designs that induce lifecycle investing, which tends to be conservative over the lifetime, therefore depend crucially on the counterfactual portfolio composition, as well as preferences and non-retirement wealth.

DSGE-Modelling: When Agents are Imperfectly Informed

DSGE-models have become important tools of analysis not only in academia but increasingly in the board rooms of central banks. The success of these models has much to do with the coherence of the intellectual framework it provides. The limitations of these models come from the fact that they make very strong assumptions about the cognitive abilities of agents in understanding the underlying model. In this paper we relax this strong assumption. We develop a stylized DSGE-model in which individuals use simple rules of thumb (heuristics) to forecast the future inflation and output gap. We compare this model with the rational expectations version of the same underlying model. We find that the dynamics predicted by the heuristic model differs from the rational expectations version in some important respects, in particular in their capacity to produce endogenous economic cycles. JEL Classification: E10, E32, D83

Repeat and Point: Differentiating semantic dementia from progressive non-fluent aphasia

To determine whether a new, simple, quick measure, the Repeat and Point test, reliably differentiates between semantic dementia (SD) and progressive non-fluent aphasia (PNFA).Fifteen patients with SD, six patients with PNFA and 18 healthy controls were administered the Repeat and Point test. Participants were required to repeat 10 multi-syllabic concrete nouns and, following each repetition, to point to the word's pictorial referent amongst an array of six semantically and perceptually similar foils.Patients with SD were consistently impaired relative to PNFA patients and controls on the comprehension (pointing) component of the task, whereas patients with PNFA showed no significant deficit on pointing but were impaired at the production (repeating) component. Discriminant function analysis confirmed perfect classification of the individual patients into their respective groups: criteria involving a ratio of the two scores are provided.The Repeat and Point test is particularly appropriate for routine use in a clinical context: it is quick and easy to administer and score; it reliably discriminated between the two patient groups, SD and PNFA; and it offers a simple rule of thumb, i.e., the Repeat-to-Point ratio, to aid in the diagnosis of these two language variants of frontotemporal dementia (FTD).

BENCHMARK TWO-GOOD UTILITY FUNCTIONS*

Benchmark two-good utility functions involving a good with zero income elasticity and unit income elasticity are well known. This paper derives utility functions for the additional benchmark cases where one good has zero cross-price elasticity, unit own-price elasticity, and zero own price elasticity. It is shown how each of these utility functions arises from a simple graphical construction based on a single given indifference curve. Also, it is shown that possessors of such utility functions may be seen as thinking in a particular sense of their utility, and may be seen as using simple rules of thumb to determine their demand.

Social Norms, Rules of Thumb, and Retirement: Evidence for Rationality in Retirement Planning

Most economists assume economic agents are well informed, far sighted, and rational. By “rational” they mean that agents use sound logic when deciding on a course of action. Rational agents combine all the information at their disposal, including knowledge of their own references and long-term interests, to make logical choices that maximize their well-being given the constraints facing them. This essay considers empirical evidence on whether this model explains saving for retirement or the timing of retirement. Many observers are skeptical that workers make retirement decisions in the far sighted and logical manner just described. Unlike other economic choices, which are repeated many times over the course of one's life, the decision of when to retire is made only once. Workers are not given the opportunity to improve on decision making through constant repetition. As an alternative to fully rational decision making, agents might imitate the behavior of others who are presumed to be better informed or to have superior skills in planning. Alternatively, workers may adopt and follow simple rules of thumb, which can produce decisions that depart significantly from a financially optimal choice. The evidence on the financial soundness of workers' retirement choices is mixed. When polled about their preparations for retirement, large minorities of Americans acknowledge they have given no thought to the subject, have saved little or nothing in pension and other retirement accounts, and lack confidence they will be able to afford retirement. Many workers near retirement age are ignorant of the rules that will determine their pension benefits. Economists and financial planners report alarming evidence that middle-aged and older workers face large saving shortfalls compared with the nest eggs needed to retire at the typical retirement age. Extensive evidence shows that a substantial minority of workers experiences big drops in consumption after they retire, which appears to violate a basic implication of the life-cycle model. On the other hand, recent analysis of the best survey evidence on workers' earnings, pension accumulations, Social Security entitlements, and non-pension saving reveals that very few workers have nest eggs that obviously and substantially fall short of what is “optimal” under some conceivably rational plan. Many workers who have little or no retirement saving can all back on Social Security or public assistance to support minimal onsumption in old age. The drop in consumption that occurs after retirement could be explained by declines in workers' consumption requirements after they leave work. Alternatively, it could be the unwelcome byproduct of a plant closing or the onset of serious disease, events that force workers to leave work early. Even if the possibility of a plant closing or poor health were fully anticipated in a far-sighted plan, the worker may have rationally intended to accept a big cut in consumption if his or her career came to a premature end. This means we cannot rule out rational foresight when workers enter retirement with little savings or when they experience big drops in consumption over the course of their retirement. Bad outcomes may have been fully anticipated – and accepted – in a far-sighted and rational retirement plan. Recent research findings on worker savings and retiree consumption do not prove that retirement and saving decisions are made in a fully rational and far-sighted way. The evidence only shows it is hard to rule out rationality and far-sightedness using available information on households' consumption and savings. What older workers actually tell us about their saving behavior, retirement plans, and knowledge of pension rules suggests that relatively few make big investments in learning or thinking about the financial trade-offs that are relevant to retirement. Many workers probably consider the payoffs from such investments to be uncertain and small. Compared with the happiness that retired workers could obtain if they followed a rational and far-sighted retirement plan, the loss in happiness they actually experience using a simpler decision-making rule may be minor.

Optimal imperfect pricing decision-making: Modifying and applying Nash's rule in a service sector context

This paper aims to demonstrate how a simple rule of thumb can form a basis to offer a rational and consistent approach to pricing decision-making when faced with (partially) unknown demand and cost functions. To this purpose Nash's decision rule (1975) is re-evaluated, modified, and applied in a service product context. The decision rule can provide management with a powerful indicator of the direction in which profit will change as the result of a change in price. It specifies the conditions under which differential pricing or discounting may be (more) profitable. In this way, the rule provides a basis for a more competitive business pricing policy. The modification to Nash's rule demonstrates that pricing can benefit from quantitative techniques which are comparatively straightforward to understand and apply. It reduces uncertainty by specifying the required elasticity of demand necessary to make change in price worthwhile. With this rule, managers have an additional tool to evaluate potential price changes in the context of particular market circumstances. The paper concludes by explaining how Nash's applied and modified rule provides an original and rational methodology for exploring whether discounting is a suitable pricing strategy for service businesses with high variable costs and inelastic demand patterns.

Systems analysis of wheat production on low water-holding soils in a Mediterranean-type environment: I. Yield potential and quality

Wheat grain yields, grain protein and grain size are often variable in a Mediterranean-type environment due to large rainfall variability. Grain yields are often low due to low N inputs as a result of large uncertainties of rainfall, particularly during the latter part of the season. Larger amounts of N fertiliser might increase yields and also grain protein in such environments but could have negative effects on grain size. A systems analysis approach was taken, using the APSIM-Nwheat crop model, to assess potential yield, grain protein concentration and grain size of wheat across a range of conditions. Rainfall and temperature varied with location. Soil type, different amounts of initial stored water and a range of management options, including varying sowing dates and N fertiliser applications, were also considered. In Australia, penalties for small grain size are based on ‘screenings’: the percentage of grain to pass through a 2 mm sieve. A new routine was developed for the model describing the relationship between screenings percentage and average simulated grain size. At low rainfall locations, 30 mm of plant-available soil water at seeding gave a significant increase in grain yield (>20%) above that for no soil water. At high rainfall locations there was little effect (<7%). Three typical coarse textured soils had similar yields at low N supplies but soils with higher plant-available water-holding capacity responded more to N applications and thus at high N applications achieved higher grain yields. Above average rainfall from May to September in combination with below average temperatures resulted in the highest simulated yields. However, seasons with an average amount of in-seasonal rainfall but with rainfall well distributed throughout the season also had above average yields. Applications of small amounts of N (30 kg N/ha) caused a slight reduction in grain protein concentration, but higher N applications (>30 kg N/ha) resulted in increased protein and screenings. Nevertheless, with moderate N (60 kg N/ha) applications and early sowing, the proportion of years with low grain protein (<10%) and low screenings (<2%) was still more than two-thirds. Simulated average yields of a location increased with average rainfall but declined with increasing average temperature of a location. This allowed the development of a simple rule of thumb in which average grain yields can be related to the rainfall/temperature index of a location. The simulation analysis showed that there is potential to increase current farmer yields through higher and split N applications on light soils in Mediterranean-type environments without increasing average screenings above 3%. However, grain protein concentrations are likely to be low in most seasons on low water-holding soils.

Prediction and evolution of transcription factors and their evolutionary families in prokaryotes

Transcription factors (TFs) play an important role in the genetic regulation of transcription in response to internal and external cellular stimulus even in a simple bacterium like Escherichia coli [1]. However little is known about their functional roles, expression dynamics and evolutionary scenarios on a large scale, even in a well studied model organisms. In this short tutorial, I will first talk about the prediction of transcription factors, which form the core of the regulatory repertoires in prokaryotes, responsible for controlling the expression of genes/transcription units by binding to their cis-regulatory regions. I will present different commonly used sequenced-based approaches to predict TFs in prokarya and discuss a simple rule of thumb to identify the putative regulatory role played by a TF based on its protein sequence alone [2-6]. I will discuss on some important properties of prokaryotic TFs which distinguish them apart from rest of the protein coding genes. The second part of the talk would concentrate on the evolutionary conservation of TFs and TF families across genomes and the implications of the observations on the phenotypic adaptation of species to different niches [3,7,8]. Finally, I will discuss some future perspectives in this area of research.

A Sectoral Analysis of Price-Setting Behavior in U.S. Manufacturing Industries

In this paper we estimate New Keynesian Phillips curves (NKPC) for U.S. manufacturing industries defined at the SIC two digit level over the period 1959 to 1996. This enables us to measure the extent of nominal inertia across industrial sectors. A key innovation in this research is the use of intermediate-goods costs rather than labor costs as a measure of marginal costs. Intermediate-goods costs are a more significant element of costs for the firms populating our sample and are not subject to the criticism that wage rates are nonallocative. We find that there is statistically significant variability in estimates of price stickiness, ranging from eight months to two years. We also find that estimates of backward-looking price-setting behavior vary, with some industries characterized by 81% of pricing decisions made in a purely forward-looking manner, while in others only 52% of pricing decisions are made that way. Market concentration (as captured by the Herfindahl-Hirschman index) appears to be associated with increased price stickiness, but reduced rule-of-thumb behavior, in setting prices. Finally, firms are also more likely to follow simple rules of thumb when output in their industry is more volatile.

Design of grouting with silica sol in hard rock – New methods for calculation of penetration length, Part I

To meet the demands laid down for recent tunnel projects in Sweden, a great deal of effort has been devoted to the grouting materials. Silica sol is a grouting material that penetrates and seals fractures where cement cannot. Studies show that in rheological terms, silica sol works differently compared with cementitious grouts and in the literature there is a lack of models to calculate the penetration lengths. In recent times there has been an increase in the use of silica sol, in major tunnel projects for example, and there is a need to understand the basics regarding its penetration in order to gain a better understanding of what can be accomplished. The fundamental difference between a gelling liquid and a cementitious grout is that initially the gelling liquid acts in the same way as a Newtonian liquid. It thus has no yield shear strength and it will continue to flow as long as there is a pressure gradient. The cementitious grout acts like a Bingham fluid, with a yield shear strength to which the penetration length can be linked. Several authors have described how the rheological models can be used to calculate the penetration length of grouts. Part I of this paper deals with how the penetration length can be computed analytically, both as 1-D channel flow and 2-D radial flow. At the end of this paper a simple rule of thumb is suggested where the penetration length is easily computed using knowledge of the hydraulic aperture and the pressure and only involving the initial viscosity of the grout and the gel induction time. In part II it is shown how the analytical models can be used to design grouting in hard rock. It also shows how the theoretical expressions are transformed into practical design criteria for grouting.

The Exercise of Options Embedded in Norwegian Student Loans

We analyze real decision making of loan holders in exercising embedded options to pay fixed or floating interest rates. The data set we use for this study is unique and covers nearly 6 million economically relevant decisions of more than $400,000$ Norwegian students between July 1999 and October 2004. Loan holders are found to follow simple rules of thumb, or heuristics, to reduce the complexity of their decision problem, but their arbitrations do not approximate well the solution of a fully rational optimization. Using a rational model we show that observed historical decisions of investors are largely suboptimal and generate significant economic losses.

Social intelligence in the spotted hyena (Crocuta crocuta).

If the large brains and great intelligence characteristic of primates were favoured by selection pressures associated with life in complex societies, then cognitive abilities and nervous systems with primate-like attributes should have evolved convergently in non-primate mammals living in large, elaborate societies in which social dexterity enhances individual fitness. The societies of spotted hyenas are remarkably like those of cercopithecine primates with respect to size, structure and patterns of competition and cooperation. These similarities set an ideal stage for comparative analysis of social intelligence and nervous system organization. As in cercopithecine primates, spotted hyenas use multiple sensory modalities to recognize their kin and other conspecifics as individuals, they recognize third-party kin and rank relationships among their clan mates, and they use this knowledge adaptively during social decision making. However, hyenas appear to rely more intensively than primates on social facilitation and simple rules of thumb in social decision making. No evidence to date suggests that hyenas are capable of true imitation. Finally, it appears that the gross anatomy of the brain in spotted hyenas might resemble that in primates with respect to expansion of frontal cortex, presumed to be involved in the mediation of social behaviour.

Quantifying the Hydrophobic Effect. 1. A Computer Simulation−Molecular-Thermodynamic Model for the Self-Assembly of Hydrophobic and Amphiphilic Solutes in Aqueous Solution

Surfactant micellization and micellar solubilization in aqueous solution can be modeled using a molecular-thermodynamic (MT) theoretical approach; however, the implementation of MT theory requires an accurate identification of the portions of solutes (surfactants and solubilizates) that are hydrated and unhydrated in the micellar state. For simple solutes, such identification is comparatively straightforward using simple rules of thumb or group-contribution methods, but for more complex solutes, the hydration states in the micellar environment are unclear. Recently, a hybrid method was reported by these authors in which hydrated and unhydrated states are identified by atomistic simulation, with the resulting information being used to make MT predictions of micellization and micellar solubilization behavior. Although this hybrid method improves the accuracy of the MT approach for complex solutes with a minimum of computational expense, the limitation remains that individual atoms are modeled as being in only one of two states-head or tail-whereas in reality, there is a continuous spectrum of hydration states between these two limits. In the case of hydrophobic or amphiphilic solutes possessing more complex chemical structures, a new modeling approach is needed to (i) obtain quantitative information about changes in hydration that occur upon aggregate formation, (ii) quantify the hydrophobic driving force for self-assembly, and (iii) make predictions of micellization and micellar solubilization behavior. This article is the first in a series of articles introducing a new computer simulation-molecular thermodynamic (CS-MT) model that accomplishes objectives (i)-(iii) and enables prediction of micellization and micellar solubilization behaviors, which are infeasible to model directly using atomistic simulation. In this article (article 1 of the series), the CS-MT model is introduced and implemented to model simple oil aggregates of various shapes and sizes, and its predictions are compared to those of the traditional MT model. The CS-MT model is formulated to allow the prediction of the free-energy change associated with aggregate formation (gform) of solute aggregates of any shape and size by performing only two computer simulations-one of the solute in bulk water and the other of the solute in an aggregate of arbitrary shape and size. For the 15 oil systems modeled in this article, the average discrepancy between the predictions of the CS-MT model and those of the traditional MT model for gform is only 1.04%. In article 2, the CS-MT modeling approach is implemented to predict the micellization behavior of nonionic surfactants; in article 3, it is used to predict the micellization behavior of ionic and zwitterionic surfactants.

MAKING REMAINING LIFE PREDICTIONS FOR BETTER PIPELINE ASSET MANAGEMENT

Most underground assets owners would like to know what the probability is for failure of a given pipeline asset as a function of material type, function type, age of the asset, geotechnical environment, and other factors, when we know past failure distributions, predominant failure mechanisms, and other attributes. While most underground utilities have collected voluminous data that could guide them into better buried asset management in the future, the use of suitable reliability analyses have been beyond their reach. Often the replacement and rehabilitation decisions have been based on simple rules of thumb rather than either good science or statistical analyses even when tremendous amount of resources and time are expended on benefiting from the use of state-of-the-art condition assessment techniques. When civil engineers struggle to convince the public and the legislators the dire need for increased rate of investments into buried assets, it is our obligation to engage the most suitable analytical tools to make the best use of past failure data and available infrastructure capex funds. This paper provides a methodology on how sound reliability analysis tools can be used in such management decisions to maintain and operate our underground assets better.

Bipolar Disorder Clinical Synthesis: Where Does the Evidence Lead?

Bipolar disorder is a common condition diagnosed by the occurrence of pathological mood elevation but most often dominated by dysphoria states. Over the past 10 years, understanding of bipolar disorder and the number of evidence-based treatments have increased dramatically. This article offers strategies for improving diagnostic confidence and simple benchmarks that facilitate integrating principles of evidence-based medicine into the management of patients with bipolar disorder. Simple systematic assessment techniques such as focusing the evaluation to assess the most extreme episode of mood elevation and longitudinal factors such as age of onset and course of illness can avoid errors of omission and raise diagnostic confidence. An iterative measurement-based treatment model that aims to bring patients and their supports into the collaborative care process for progressively better outcomes is recommended.

The salinity tolerance of freshwater macroinvertebrate eggs and hatchlings in comparison to their older life-stages: a diversity of responses

The tolerance to high salinity of older life stage macroinvertebrates could underestimate the effects of increasing salinity on freshwater macroinvertebrates. The salinity tolerance of the eggs and/or hatchlings of Glyptophysa gibbosa (Planorbidae), Glyptophysa aliciae, Glacidorbis sp. (Glacidorbidae), a Glossiponiidae, Piona cumberlandis (Pionidae), and Chironomus sp. (Chironomidae) were determined. The salinity tolerances of younger life-stages of species studied here and elsewhere were then compared to salinity tolerances of their mature aquatic or dominant life-stage. A diversity of responses have been observed with some species having similar salinity tolerances in all life-stages examined, whilst the eggs or hatchlings of other species had salinity tolerances ranging from 4% to 88% of their older life stages. On present knowledge, this diversity of responses presents some difficulties for simple rules of thumb to approximate sensitivity of young life-stages of freshwater macroinvertebrates inferred from their dominant stage’s tolerance.