Estimating reliability coefficients with heterogeneous item weightings using Stata: A factor based approach

We show how to estimate a Cronbach's alpha reliability coefficient in Stata after running a principal component or factor analysis. Alpha evaluates to what extent items measure the same underlying content when the items are combined into a scale or used for latent variable. Stata allows for testing the reliability coefficient (alpha) of a scale only when all items receive homogenous weights. We present a user-written program that computes reliability coefficients when implementation of principal component or factor analysis shows heterogeneous item loadings. We use data on management practices from Bloom and Van Reenen (2010) to explain how to implement and interpret the adjusted internal consistency measure using afa.afa, factor analysis, Cronbach's alpha, reliability, heterogeneous scale construction,latent variable

Gravity Models of Trade-based Money Laundering

Several attempts have been made in the economics literature to measure money laundering. However, the adequacy of these models is difficult to assess, as money laundering takes place secretly and, hence, goes unobserved. An exception is trade- based money laundering (TBML), a special form of trade abuse that has been discovered only recently. TBML refers to criminal proceeds that are transferred around the world using fake invoices that under- or overvalue imports and exports. This article is a first attempt to test well-known prototype models proposed by Walker and Unger to predict illicit money laundering flows and to apply traditional gravity models borrowed from international trade theory. To do so, we use a dataset of Zdanowicz of TBML flows from the US to 199 countries. Our test rejects the specifications of the Walker and Unger prototype models, at least for TBML. The traditional gravity model that we present here can indeed explain TBML flows worldwide in a plausible manner. An important determinant is licit trade, the mass in which TBML is hidden. Furthermore, our results suggest that criminals use TBML in order to escape the stricter anti money laundering regulations of financial markets.Money laundering, international trade, gravity model, Walker model.

Mission-specific drive cycles to evaluate the brake energy recovery on refrigerated semitrailers

Die stetig zunehmende Bedeutung des Kraftstoffverbrauchs schwerer Nutzfahrzeuge im Straßengütertransport bezüglich Betriebskosten, Ressourcenverbrauch und CO2-Emissionen führt zur Entwicklung immer effizienterer Fahrzeuge und Fahrzeugkombinationen, wobei erreichbare Verbrauchseinsparungen vom tatsächlichen Fahrzeugeinsatz beim Anwender abhängen. Um im Rahmen des Entwicklungsprozesses oder bei der Konfiguration entsprechender Fahrzeuge simulationsgestützte Aussagen zu anwenderspezifischen Einsparpotentialen treffen zu können, sind geeignete einsatzindividuelle Fahrzyklen erforderlich. Standardisierte Fahrzyklen sind hierzu nicht geeignet, da in der Regel eine Abweichung zwischen dem beschriebenen und dem tatsächlichen Einsatz beim Fahrzeugbetreiber besteht. Die vorliegende Arbeit greift diese Problematik auf und stellt eine Methode zur automatischen Erzeugung einsatzindividueller Fahrzyklen vor. Diese Fahrzyklen sind zur Nachbildung beliebiger Einsatzprofile schwerer Nutzfahrzeuge im Straßengütertransport geeignet und lassen sich zur Simulation des Fahrzeugbetriebs verwenden. Zur Gewährleistung aussagekräftiger und vergleichbarer Ergebnisse geben die Fahrzyklen eine Zielgeschwindigkeit und die Fahrbahnsteigung jeweils über dem Weg vor. Ergänzend sind der Zielgeschwindigkeit kurzzeitige Verzögerungs- und Haltevorgänge in Form sogenannter Events überlagert. Zusätzlich beinhalten die Fahrzyklen einsatzindividuelle Ladevorgänge und den daraus resultierenden variablen Verlauf der Zuladung über der Fahrt. Die Erzeugung der Fahrzyklen basiert auf einer formalen Beschreibung des jeweiligen Fahrzeugeinsatzes und einer hinterlegten Datenbasis. Als Anwendungsbeispiel dient die Bremsenergierückgewinnung am Kühlsattelauflieger zur elektrischen Versorgung des ansonsten dieselmotorisch betriebenen Kühlaggregats. Aufbauend auf der einleitenden Darstellung existierender Fahrzyklen und veröffentlichter Ansätze zu deren Erzeugung werden die im Rahmen dieser Arbeit entwickelte simulationsbasierte Methode und die Algorithmen zur Generierung der angestrebten einsatzindividuellen Fahrzyklen ausführlich erläutert. Zur nachfolgenden Validierung der Methode und Fahrzyklen wird auf Messergebnisse zur Bremsenergierückgewinnung am Kühlsattelauflieger zurückgegriffen, die mit einem aufgebauten Versuchsträger in Fahrversuchen gewonnen wurden. Anhand des Abgleichs der Mess- und entsprechend generierter Simulationsergebnisse für ausgewählte Testfahrten konnte die Eignung der Fahrzyklen zur einsatzindividuellen Bewertung der Bremsenergierückgewinnung am Kühlsattelauflieger erfolgreich nachgewiesen werden. Mit diesem Ergebnis wird die Methode abschließend zur Dimensionierung des Bremsenergierückgewinnungssystems für zwei exemplarische und realitätsnahe Einsatzprofile angewandt.The increasing importance of fuel consumption for road freight transport in terms of operating costs, finite resources and CO2 emissions leads to the development of ever more efficient vehicles and vehicle combinations. Possible fuel savings however depend on the actual use i.e. the mission profile of the vehicles by the user, which is amongst others characterized by different route lengths, chosen road types, varying payloads and regional operating conditions such as topography. Thus to determine user specific savings within the product development process or while configuring vehicles corresponding mission-specific drive cycles are required. The possibility to apply standardized drive cycles for this purpose is limited, as the vehicle operation described by the drive cycle and the user specific operation typically differ. Against this background a method to automatically generate mission-specific drive cycles is proposed. The drive cycles can be applied in vehicle simulations and are capable to describe arbitrary mission profiles of heavy duty vehicles in road freight transport. To ensure representative and comparable results the generated drive cycles provide a distance based target speed and road slope. Short-term decelerations, stops and loading as well as unloading processes are additionally superimposed as so-called events. Thereby variable and mission-specific payloads can be described by the drive cycle. The generation of the drive cycles is based on a formal description of the particular mission profile and a previously set up data base, which contains statistics characterizing the target speed, slope and event distribution. The recovery of brake energy on refrigerated semitrailers to electrically supply the otherwise diesel-driven cooling unit serves as example. Based on the presentation of existing drive cycles and published approaches for their generation the method developed within this thesis is derived. At the same time the overall simulation-based approach and the algorithms for the generation of the mission-specific drive cycles are explained in detail. To demonstrate the feasibility of the brake energy recovery on refrigerated semitrailers and to determine the saving potentials several real world test runs were conducted with a built-up research vehicle. The gathered data and results are subsequently applied to validate the method and the generated drive cycles. By comparing the measured and simulated amounts of recovered energy for specific test runs the suitability of the generated drive cycles for the evaluation of corresponding systems was successfully proven. Finally the developed method is applied to generate drive cycles for exemplary and realistic mission profiles. These drive cycles are then used to identify mission-specific configurations for a brake energy recovery system on semitrailers

Systematic review and meta-analysis: rapid diagnostic tests versus placental histology, microscopy and PCR for malaria in pregnant women

<p>Abstract</p> <p>Background</p> <p>During pregnancy, malaria infection with <it>Plasmodium falciparum </it>or <it>Plasmodium vivax </it>is related to adverse maternal health and poor birth outcomes. Diagnosis of malaria, during pregnancy, is complicated by the absence or low parasite densities in peripheral blood. Diagnostic methods, other than microscopy, are needed for detection of placental malaria. Therefore, the diagnostic accuracy of rapid diagnostic tests (RDTs), detecting antigen, and molecular techniques (PCR), detecting DNA, for the diagnosis of <it>Plasmodium </it>infections in pregnancy was systematically reviewed.</p> <p>Methods</p> <p>MEDLINE, EMBASE and Web of Science were searched for studies assessing the diagnostic accuracy of RDTs, PCR, microscopy of peripheral and placental blood and placental histology for the detection of malaria infection (all species) in pregnant women.</p> <p>Results</p> <p>The results of 49 studies were analysed in metandi (Stata), of which the majority described <it>P. falciparum </it>infections. Although both placental and peripheral blood microscopy cannot reliably replace histology as a reference standard for placental <it>P. falciparum </it>infection, many studies compared RDTs and PCR to these tests. The proportion of microscopy positives in placental blood (sensitivity) detected by peripheral blood microscopy, RDTs and PCR are respectively 72% [95% CI 62-80], 81% [95% CI 55-93] and 94% [95% CI 86-98]. The proportion of placental blood microscopy negative women that were negative in peripheral blood microscopy, RDTs and PCR (specificity) are 98% [95% CI 95-99], 94% [95% CI 76-99] and 77% [95% CI 71-82]. Based on the current data, it was not possible to determine if the false positives in RDTs and PCR are caused by sequestered parasites in the placenta that are not detected by placental microscopy.</p> <p>Conclusion</p> <p>The findings suggest that RDTs and PCR may have good performance characteristics to serve as alternatives for the diagnosis of malaria in pregnancy, besides any other limitations and practical considerations concerning the use of these tests. Nevertheless, more studies with placental histology as reference test are urgently required to reliably determine the accuracy of RDTs and PCR for the diagnosis of placental malaria. <it>P. vivax</it>-infections have been neglected in diagnostic test accuracy studies of malaria in pregnancy.</p

The stimulative effect of an unconditional block grant on the decentralized provision of care

Understanding the impact of central government grants on decentralized healthcare provision is of crucial importance for the design of grant systems, yet empirical evidence on the prevalence of flypaper effects in this domain is rare. We study the decentralization of home care in the Netherlands and exploit the gradual introduction of formula-based equalization to identify the effect of exogenous changes in an unconditional block grant on local expenditure and utilization. A one euro increase in central government grants raises local expenditure by twenty to fifty cents. Adjustments occur through the number of hours as well as through substitution between basic and more advanced types of assistance. These findings suggest that conditioning of grants is not required for the central government to retain a moderate degree of control over the decentralized provision of care