MULTIPLIER ESTIMATES: TO BIAS OR NOT TO BIAS?*

ABSTRACT It is well known that multiplier estimates within an interindustry context may be biased when the input coefficients are stochastic. Several conditions have been derived under which the estimates were shown to be biased, all with the same sign. In contrast to these analytical results, however, simulations using a stochastic transactions table unexpectedly reported the unbiasedness of multiplier estimates. This note argues that the sample sizes were too small. It is shown that for increased sample sizes the multiplier estimates are all positively and significantly biased, in line with the analytical results, but the biases are very small.     

Assessment of Numerical and Experimental Errors in Hybrid Simulation of Framed Structural Systems through Collapse

Hybrid simulation can provide significant advantages for large-scale experimental investigations of the seismic response of structures through collapse, particularly when considering cost and safety of conventional shake table tests. Hybrid simulation, however, has its own challenges and special attention must be paid to mitigate potential numerical and experimental errors that can propagate throughout the simulation. Several case studies are presented here to gain insight into the factors influencing the accuracy and stability of hybrid simulation from the linear-elastic response range through collapse. The hybrid simulations were conducted on a four-story two-bay moment frame with various substructuring configurations. Importantly, the structural system examined here was previously tested on a shake table with the same loading sequence, allowing for direct evaluation of the hybrid simulation results. The sources of error examined include: (1) computational stability in numerical substructure; (2) setup and installation of the physical specimen representing the experimental substructure; and (3) the accuracy of the selected substructuring technique that handles the boundary conditions and continuous exchange of data between the subassemblies. Recommendations are made regarding the effective mitigation of the various sources of errors. It is shown that by controlling errors, hybrid simulation can provide reliable results for collapse simulation by comparison to shake table testing.     

Model Uncertainty in Matrix Exponential Spatial Growth Regression Models

This article considers the most important aspects of model uncertainty for spatial regression models, namely, the appropriate spatial weight matrix to be employed and the appropriate explanatory variables. We focus on the spatial Durbin model (SDM) specification in this study that nests most models used in the regional growth literature, and develop a simple Bayesian model‐averaging approach that provides a unified and formal treatment of these aspects of model uncertainty for SDM growth models. The approach expands on previous work by reducing the computational costs through the use of Bayesian information criterion model weights and a matrix exponential specification of the SDM model. The spatial Durbin matrix exponential model has theoretical and computational advantages over the spatial autoregressive specification due to the ease of inversion, differentiation, and integration of the matrix exponential. In particular, the matrix exponential has a simple matrix determinant that vanishes for the case of a spatial weight matrix with a trace of zero. This allows for a larger domain of spatial growth regression models to be analyzed with this approach, including models based on different classes of spatial weight matrices. The working of the approach is illustrated for the case of 32 potential determinants and three classes of spatial weight matrices (contiguity‐based, k‐nearest neighbor, and distance‐based spatial weight matrices), using a data set of income per capita growth for 273 European regions.     

Modeling the Uncertainty of Slope and Aspect Estimates Derived from Spatial Databases

Estimates of slope and aspect are commonly made from digital elevation models (DEMs), and are subject to the uncertainty present in such models. We show that errors in slope and aspect depend on the spatial structure of DEM errors. We propose a general-purpose model of DEM errors in which a spatially auto-regressive random field is added as a disturbance term to elevations. In addition, we propose a general procedure for propagating such errors through GIS operations. In the absence of explicit information on the spatial structure of DEM errors, we demonstrate the potential utility of a worst-case analysis. A series of simulations are used to make general observations about the nature and severity of slope and aspect errors.     

Statistical errors in the determination of wind velocities by the spaced antenna technique

This paper is concerned with the statistical errors which are present when wind velocities in the atmosphere are determined by the radar method known as the spaced antenna technique. It is assumed that the (complex) data is processed by the method known as full correlation analysis (FCA). A theory is first developed to give the error in the determination of the position of the maximum of a cross-correlation function and the value of lag such that the auto-correlation falls to a value equal to that of the crosscorrelation at zero lag. These are the basic quantities needed for the application of FCA. These error estimates are tested with a variety of numerically simulated data and shown to be realistic. The results are applied to real data and, using the standard techniques for the propagation of errors, they lead to estimates of the errors in the derived wind velocities. In order to test these estimates, an experiment was carried out in which two independent wind determinations were made simultaneously. The differences were used to obtain experimental estimates of the errors. It was found that the theory overestimates the error in the wind velocities by about 50%. Possible reasons for this are discussed.     

The estimation of the relative frequencies of mammalian species: Khirokitia 1972

The difficulties in the estimation of relative frequencies of species are discussed and a new approach to the recording of bone is proposed. This approach eliminates various biases and allows minimum numbers of individuals and counts of identified specimens to be derived from the same data. Sieved material from Khirokitia is used to provide a comparison of different methods and to illustrate possible ways of recording the information.     

System failure: the underlying causes of US policy‐making errors in Afghanistan

The United States intervention in Afghanistan since 2001 has brought progress in some areas, but the conflict has expanded, the Taliban remains powerful, and misgovernance and predation are widespread. Afghan national security forces—the linchpin of the coalition's exit strategy—offer no guarantee of future stability. Many accounts describe the mistakes that led to this predicament. This article attempts to explain why these mistakes were made by examining their underlying or structural causes. Based on 51 interviews with officials and experts, it identifies major US policy‐making errors with respect to state‐building, military activities and diplomacy. It argues that there are four principal underlying causes of such errors, relating to organizations, leadership and strategic thinking, psychology, and domestic politics. It finds that there were severe shortcomings in the acquisition and processing of information and a lack of institutional self‐evaluation; civilian and military leaders made major strategic misjudgements in mistaking the strategy for the goal, overestimating the efficacy of military force or resources, and drawing false lessons from history or analogous cases such as Iraq; leaders were predisposed to overconfidence and oversimplification; and, at the highest level, policies were distorted by domestic politics. The article contends that the cumulative impact of these shortcomings was sufficient to seriously disrupt the functioning of the foreign policy‐making system. It argues that action is required to improve US information gathering and assessment, systematize institutional self‐evaluation, build regional expertise, establish mechanisms to understand the motivations and perceptions of other actors, and increase awareness of decision‐makers’ cognitive flaws and biases.     

X-RAY FLUORESCENCE ANALYSIS OF MUSEUM OBJECTS: A NEW INSTRUMENT

A new X-ray fluorescent analyser is described which uses a miniature X-ray tube or radioisotope source as alternative means of primary excitation. The advantages of this approach as compared to previous methods, particularly where elements low in the periodic table are concerned, is discussed. The second part of the paper describes an application of the technique. The non-destructive analysis of valuable ceramics, where elements low in the periodic table are important for differentiation purposes, has previously presented a problem. By using the ‘Isoprobe’such measurements are possible. In this instance the separation of early Chinese porcelains into Northern and Southern production groups is shown to be possible. Although samples have been ground from the wares for comparison with optical emission spectrometry, it is shown that analysis of the unglazed portions of the pots themselves gave similar results.     

Heterogeneity of Attribute Sampling Error in Spatial Data Sets

This paper considers the standard error of the estimate of the mean of a spatially correlated variable in the case where data are obtained by a process of random sampling. Two distinct mean estimation problems are identified: estimating the area mean and estimating the population mean. Methods are described for obtaining standard error estimates in the two cases and, within the limits of publicly available information, the methods are implemented on average household income data at the census tract scale for Syracuse, New York. The purpose of the paper is to draw attention to issues of data precision in relation to sampled geographic information on averages and in particular to consider the problems of estimating standard errors using such data. The paper also examines the extent to which standard errors vary between census tracts.     

THE MOSES-PREDOHL PULL AND THE LOCATION DECISION OF THE FIRM*

ABSTRACT This paper exploits the two-stage approach and the envelope theorem to examine the role of the Moses-Predhol pull in the cost-minimizing location theory of the firm. It shows that the two-stage approach introduces the Moses-Predohl pull into the first-order conditions. The Moses-Predohl pull is shown to be equal to zero through the envelope theorem. These results show why the assertions of Bossert and Buhl (1986) concerning Kusumoto (1984,1985) are incorrect.     

Direct Acceleration Feedback Control of Shake Tables with Force Stabilization

This study presents a new strategy for shake table control that uses direct acceleration feedback without need for displacement feedback. To ensure stability against table drift, force feedback is incorporated. The proposed control strategy was experimentally validated using the shake table at the Johns Hopkins University. Experimental results showed that the proposed control strategy produced more accurate acceleration tracking than conventional displacement-controlled strategies. This article provides the control architecture, details of the controller design, and experimental results. Furthermore, the impact of input errors in shake table testing on the structural response is also discussed.     

Probabilistic Regionalization via Evidence Accumulation with Random Spanning Trees as Weak Spatial Representations

Spatial clusters contain biases and artifacts, whether they are defined via statistical algorithms or via expert judgment. Graph-based partitioning of spatial data and associated heuristics gained popularity due to their scalability but can define suboptimal regions due to algorithmic biases such as chaining. Despite the broad literature on deterministic regionalization methods, approaches that quantify regionalization probability are sparse. In this article, we propose a local method to quantify regionalization probabilities for regions defined via graph-based cuts and expert-defined regions. We conceptualize spatial regions as consisting of two types of spatial elements: core and swing. We define three distinct types of regionalization biases that occur in graph-based methods and showcase the use of the proposed method to capture these types of biases. Additionally, we propose an efficient solution to the probabilistic graph-based regionalization problem via performing optimal tree cuts along random spanning trees within an evidence accumulation framework. We perform statistical tests on synthetic data to assess resulting probability maps for varying distinctness of underlying regions and regionalization parameters. Lastly, we showcase the application of our method to define probabilistic ecoregions using climatic and remotely sensed vegetation indicators and apply our method to assign probabilities to the expert-defined Bailey's ecoregions.     

Eigenvector Spatial Filtering for Large Data Sets: Fixed and Random Effects Approaches

Eigenvector spatial filtering (ESF) is a spatial modeling approach, which has been applied in urban and regional studies, ecological studies, and so on. However, it is computationally demanding, and may not be suitable for large data modeling. The objective of this study is developing fast ESF and random effects ESF (RE‐ESF), which are capable of handling very large samples. To achieve it, we accelerate eigen‐decomposition and parameter estimation, which make ESF and RE‐ESF slow. The former is accelerated by utilizing the Nyström extension, whereas the latter is by small matrix tricks. The resulting fast ESF and fast RE‐ESF are compared with nonapproximated ESF and RE‐ESF in Monte Carlo simulation experiments. The result shows that, while ESF and RE‐ESF are slow for several thousand samples, fast ESF and RE‐ESF require only several seconds for the samples. It is also suggested that the proposed approaches effectively remove positive spatial dependence in the residuals with very small approximation errors when the number of eigenvectors considered is 200 or more. Note that these approaches cannot deal with negative spatial dependence. The proposed approaches are implemented in an R package “spmoran.”     

Error sources and travel time residuals in plasmaspheric whistler interpretation

In the interpretation of observed whistlers by curve fitting, systematic travel time residuals appeared which were studied by extensive simulations using ray-tracing, numerical integration and curve fitting. The residuals were found to originate from the commonly used approximations in the refractive index and ray path of whistler mode waves, which result in travel time increments or decrements, not accounted for in whistler interpretation. These approximations and the assumed form of the electron density distribution also lead to systematic errors in the diagnostics of plasmaspheric electron density by whistlers. In addition, the effects of other error sources, including random measurement errors, are also reviewed briefly.It is shown that the fine structure of residual curves is connected to propagation conditions. Thus, their study may yield a new research tool for studying whistler trapping, ducting structures and other features of whistler propagation. The application of residual analysis in conjunction with digital matched filtering of whistlers seems to be especially promising for further whistler studies.     

THE POLICY PROCESS AND ORGANIZATIONAL FORM

In this paper the transactions cost approach (TCA) is used to define organizations and to predict their forms under certain conditions. Next, Aaron Wildavsky's approach is used to define the policy process and to predict its form in particular organizations. Two assertions follow: namely, that the most efficient organizational form may be predicted from knowledge of underlying transactions costs, and that the form of the policy process in an organization can be predicted from knowledge of the organization's form (regardless of whether it is the most efficient form). Recent natural gas policy in the U.S.A. is used to illustrate these propositions, and several conclusions are offered about 1) the potential applicability of the TCA to the public sector and to the policy process and 2) about the potential applicability of Wildavsky's version of the policy process to differing organizational forms.     

Life tables in palaeodemography: A methodological note

Several errors in the early literature discussing life-table analysis of skeletal populations are potentially misleading to the researcher unacquainted with the mathematical methods of palaeodemography. Additional errors document the hazards of borrowing life-table methods and equations from other applications without fully realizing their context, interpretation, and the potential restrictions on their use. A simple generalization of the life-table equations explicitly to reveal their dependence on the entry age and width of the age intervals used will facilitate the correct computation of life tables and readily accommodate the use of unconventional or otherwise non-standard cohorts. A general procedure for computing a life table for a skeletal population is presented, and a numerical example is included to illustrate the method.     

Coherent-array HF Doppier sounding of traveling ionospheric disturbances: II. Assessment of errors

We examine errors which are likely to occur in the compact-array HF sounding technique for determining the velocity of traveling ionospheric disturbances. The errors arise from ionospheric irregularities (either large-scale specular facets, or fine-scale scatterers) and from the presence of multiple disturbance undulations propagating simultaneously with different velocities. The errors are either systematic (that is, not causing internal inconsistencies within the array velocimetry data) or random (that is, causing quantifiable inconsistencies between alternative velocity estimates furnished by the array). The random errors can be directly assessed using array data, as is illustrated for actual data from a 16-channel array.     

RAS‐ING THE TRANSACTIONS OR THE COEFFICIENTS: IT MAKES NO DIFFERENCE*

ABSTRACT The biproportional RAS technique has become one of the most important tools to update, regionalize, or balance input–output tables. In this note, we rigorously prove that the estimation of the intermediate transactions matrix yields the same results as the estimation of the input coefficients matrix or the output coefficients matrix. We also show that this does not hold for any of the other updating procedures that have been commonly proposed as an alternative to RAS.     

The role of gender norms in access to agricultural training in Chikwawa and Phalombe,Malawi

Based on qualitative research conducted in Chikwawa and Phalombe in Malawi, this article discusses how gender relations shape men and women’s access to and participation in agricultural training. It also examines how men and women justify or challenge gender inequalities in relation to access to agricultural information and knowledge. Data on gender and recruitment to and participation in training, barriers to training and access to information as well as farmer to farmer extension models were collected and analysed. A gender relations approach, focusing on power and inequality, was used to analyse the data. The data shows that the perception of men as household heads and women as carers or helpers who are also illiterate and ignorant often has implications on women’s ability to access training and information. Negative stereotypical perceptions about women by their husbands and extension workers militate against women’s access to training and information. Institutional biases within extension systems reproduce gender inequality by reinforcing stereotypical gender norms. Extension officers should be targeted with training on gender responsive adult learning methodologies and gender awareness to help them be more inclusive and sensitive to women’s needs.     

The effect of a priori knowledge on parameter estimation errors with applications to incoherent scatter

The dependence of the width of the a posteriori distribution (i.e. parameter estimation error) in a multiparameter fit on the a priori width of another parameter is studied in the framework of linear statistical inversion theory. An exact formula is given which makes it possible to estimate how accurate the a priori information on a given parameter must be in order to obtain the other parameter with a prescribed accuracy. These estimates are useful in those cases where some errors are strongly correlated, like the ion temperature and the O⁺ content in incoherent scatter measurements with the EISCAT UHF radar. The dependence of the solution on the accuracy of the power profile estimates is given. Likewise, the behaviour of the error when a linear combination of the parameters is known exactly is given. The formulae given have a very simple geometrical meaning, and together they give a complete solution to the problem of estimating the accuracies in a multiparameter fit when a linear combination of the variables is known with a prescribed accuracy. It is shown that under the conditions considered in this paper, oxygen content can be determined to an accuracy of 10 % when the ion temperature is known to within 7 %, if we can assume that the collision frequency is zero.