Maintaining the Regular Ultra Passum Law in data envelopment analysis

The variable returns to scale data envelopment analysis (DEA) model is developed with a maintained hypothesis of convexity in input-output space. This hypothesis is not consistent with standard microeconomic production theory that posits an S-shape for the production frontier, i.e. for production technologies that obey the Regular Ultra Passum Law. Consequently, measures of technical efficiency assuming convexity are biased downward. In this paper, we provide a more general DEA model that allows the S-shape.Data envelopment analysis; homothetic production; S-shaped production function; non-convex production set

Testing over-representation of observations in subsets of a DEA technology

This paper proposes a test for whether data are over-represented in a given production zone, i.e. a subset of a production possibility set which has been estimated using the non-parametric Data Envelopment Analysis (DEA) approach. A binomial test is used that relates the number of observations inside such a zone to a discrete probability weighted relative volume of that zone. A Monte Carlo simulation illustrates the performance of the proposed test statistic and suggests good estimation of both facet probabilities and the assumed common inefficiency distribution in a three dimensional input space.Data Envelopment Analysis (DEA); Over-representation; Data density; Binomial test; Convex hull

Måling af produktivitet over tid: det metodiske grundlag for dynamisk benchmarking i DEA

Dynamisk benchmarking vedrører måling af ændringer i produktivitet over tid, som kan beskrives ved et Total Factor Productivity indeks. Dette indeks beskriver nettoeffekten af i) ændringer i best practice og ii) catching up effekten defineret som ændringen i den enkelte virksomheds positionering i forhold til best practice. I den foreliggende artikel beskrives, hvordan Data Envelopment Analysis kan benyttes til estimation af et Total Factor Productivity indeks, og hvordan dette indeks kan dekomponeres multiplikativt i to delkomponenter, der beskriver ændringer i best practice hhv. catching up effekter. Der gives en geometrisk intuition for dekomponeringen suppleret med et taleksempel og en mere matematisk stringent fremstilling

Måling af produktivitet over tid: det metodiske grundlag for dynamisk benchmarking i DEA

Dynamisk benchmarking vedrører måling af ændringer i produktivitet over tid, som kan beskrives ved et Total Factor Productivity indeks. Dette indeks beskriver nettoeffekten af i) ændringer i best practice og ii) catching up effekten defineret som ændringen i den enkelte virksomheds positionering i forhold til best practice. I den foreliggende artikel beskrives, hvordan Data Envelopment Analysis kan benyttes til estimation af et Total Factor Productivity indeks, og hvordan dette indeks kan dekomponeres multiplikativt i to delkomponenter, der beskriver ændringer i best practice hhv. catching up effekter. Der gives en geometrisk intuition for dekomponeringen suppleret med et taleksempel og en mere matematisk stringent fremstilling

Pendlingens sociale geografi: Transportmiddelvalg i lyset af pendlerens politiske holdninger, sociale normer og kultur

Danske pendlere kører fortrinsvist i bil – også i store byer som København. Når rejsetiden er 20 minutter i bil var der blandt pendlere bosiddende i Hovedstaden godt 15 % cyklister, 35 % bilister og 15 % i offentlig transport. De resterende 35 % var enten til fods eller vekslede mellem forskellige transportmidler fra dag til dag. Tilsvarende ved 20 minutter var andelene blandt sjællændere godt 5 % cyklister, 55 % bilister og godt 5 % i offentlig transport. Region Nord- og Midtjylland havde begge 5 % på cykel, 75 % i bil og 5 % i offentlig transport. I Syddanmark sås ved 20 minutters rejsetid 10 % cyklister, 60 % i bil og 5 % i bus/tog. Beregningerne er baseret på data fra en spørgeskemaundersøgelse blandt 2235 pendlere. Vi estimerede elasticitet i transportmiddelvalget med hensyn til rejsetid i bil. Rejsetiderne blev beregnet ved brug af Google Maps Distance Matrix. Pendlerne var alle i beskæftigelse, 18-65 år og med samme fordeling af køn, alder, geografi og uddannelse, som den danske baggrundsbefolkning. Desuden præsenteres en typologi afpendlere, der indeholder 4 overordnede grupperinger. “Bilister uden klare holdninger” (32 %), “grønne pendlere i storbyen” (30 %), “bilister der bor uden for de store byer” (23 %) og endelig ”anti-grønne bilister” (15 %). Denne opdeling i pendler-grupperinger indeholdt overraskende få holdninger og kultur

Does Retrograde Femoral Nailing through a Normal Physis Impair Growth?:An Experimental Porcine Model

MATERIALS AND METHODS: The study was carried out using an experimental porcine model. Eleven juvenile female porcines were randomized for insertion of a retrograde femoral nail in one limb. The other limb acted as a control. The animals were housed for 8 weeks before the nail was removed and housed for 8 additional weeks, that is, 16 weeks in total. Growth was assessed by interphyseal distance on 3D magnetic resonance imaging (MRI) after 16 weeks and the operated limb was compared to the non-operated limb. Histomorphometric analysis of the physeal canal was performed. RESULTS: No difference in longitudinal growth was observed when comparing the operated femur to the non-operated femur using MRI after 16 weeks. No osseous tissue crossing the physis was observed on MRI or histology. The empty canal in the physis after nail removal was filled with fibrous tissue 16 weeks after primary surgery. CONCLUSION: Growth was not impaired and no bone bridges were seen on MRI or histology 16 weeks after insertion and later removal of the retrograde femoral nail. CLINICAL SIGNIFICANCE: The insertion of a retrograde intramedullary femoral nail centrally through the physis and later removal might be safe, however, long-term follow-up is needed. AIM AND OBJECTIVE: The insertion of an intramedullary nail may be beneficial in certain cases of leg length discrepancy (LLD) in children. However, it is unknown if the physeal injury due to the surgery may cause bone bridge formation and thereby growth arrest after removal. This study aimed to assess longitudinal interphyseal growth 16 weeks after insertion and later removal of a retrograde femoral nail passing through the physis. Moreover, to analyse the tissue forming in the empty physeal canal after removal of the nail. HOW TO CITE THIS ARTICLE: Abood AA, Rahbek O, Olesen ML, et al. Does Retrograde Femoral Nailing through a Normal Physis Impair Growth? An Experimental Porcine Model. Strategies Trauma Limb Reconstr 2021;16(1):8–13