Publications

Waste sorting is an important recovery process in circular product systems. Engineering sciences deal with its performance measurement by analysing various parameter settings based on technical key figures derived from object and component quantities. They are difficult to aggregate, especially since there are no prices for all inputs and outputs. Data Envelopment Analysis (DEA) allows an aggregation without implementing prices or weight restrictions. This paper shows how DEA can be used as performance measurement method for sorting processes, whose purpose it is to separate different material components from a waste mixture as effectively and efficiently as possible. This is achieved when the individual components are sorted out into their respective recycling bins with as little effort as possible and without allowing too many incorrect throws. In this respect, sorting processes represent pure material reallocations - and no material transformations. Thus, valid material balances of sorting technologies do not allow for free disposability. A new multiple criteria DEA approach is suggested, which uses input and output objects that entirely consist of components determining the object's value. Different from common DEA approaches, the technological perspective of modelling the underlying production system is strictly separated from the preference perspective of modelling multiple performance criteria for the relevant input and output types and sorts. In more detail, we develop DEA models for a combined evaluation of operating and quality efficiency where both inputs and outputs are characterised by sorts or grades of varying quality. In contrast to existing approaches that map quality into DEA we reflect upon the underlying technological assumptions and analyse which dominance relations result from that in our case of waste sorting.

Joint production is a term with a long history in economics, encompassing a variety of ubiquitous production types that usually generate both main products as well as desirable and undesirable byproducts. However, studies in economic history show that important phenomena subsumed under this term were largely ignored by the theories of general economics and of business economics in the twentieth century. Our systematic, narrative literature review based on the Web of Science analyses the extent to which this and other terms corresponding to such phenomena have been taken up by researchers since then. Whereas the number of papers on undesirable outputs has soared, especially in the past decade, the economic literature regarding joint production and harmless byproducts is much smaller and hardly growing. This is in stark contrast to their relevance in practice, recorded in the non-economic literature. Harmful byproducts result from coupled production, as a rule. However, this important manifestation of joint production is usually not distinguished from other specific types. In German-language literature, coupled production is defined as a kind of (truly) joint production in which an intended product cannot be manufactured without an additional type of output under consideration. Our review reveals a lack of clarity, precision, and consistency in the use of established terms and concepts in English-language literature, that may lead to insufficient external validity of widely accepted models. Moreover, one gets the impression that academic disciplines concerned with business or general economics focus too much on problems that are currently of economic interest, while neglecting other issues that may be marginal today but are likely to be of critical importance in the near future.

Accounting, life cycle assessment (LCA) and data envelopment analysis (DEA) are examples of various research areas that independently develop and apply diverse methodologies to evaluate performance. Though, many methods have in common that the results to be assessed are mainly determined by the inputs and outputs of the activities which are to be evaluated. Based on both production and decision theory, our comprehensive framework integrates and systematically distinguishes specific types of production-based performance assessment. It allows to examine and categorise the existing literature on such approaches. Our review focuses on sources which explicitly apply concepts or methods of multiple criteria decision analysis (MCDA). We did not find any elaborated methodology that fully integrates MCDA with production theory. At least, a basic approach to multicriteria performance analysis, which generalises the methodology of data envelopment analysis, appears to be well-grounded on production theory. It was already presented in this journal in 2001 and has rarely been noticed in the literature until now. A short overview outlines its recent insights and main findings. A key finding is that a category mistake prevails among well-known methodologies of efficiency measurement like DEA. It may imply invalid empirical results because the inputs and outputs of production processes are confused with resulting impacts destroying or creating values (to be minimised or maximised, respectively). We conclude by defining open problems and by indicating prospective research directions.

In der aktuellen Diskussion um Alternativen zum privaten Fahrzeugbesitz spielen nachhaltige Mobilitätskonzepte wie Car- und Bikesharing-Systeme eine zentrale Rolle. Ihre Akzeptanz wird maßgeblich durch eine adäquate raum-zeitliche Verfügbarkeit der Fahrzeuge bestimmt. Daher stellt aus Anbietersicht die Fahrzeugverfügbarkeit das zentrale Planungsproblem dar. In der sozialwissenschaftlichen Forschung wird dies vor allem durch Erklärungs-und Entscheidungsmodelle zur Lösung von Managementaufgaben erfasst. Die Modelle fokussieren zumeist praxisnahe Teilaspekte der Fahrzeugverfügbarkeit, ohne das Planungsproblem in seiner Gesamtheit theoretisch zu untermauern. Daher wird in der vorliegenden Arbeit ein generisches Rahmenmodell entwickelt, durch das ö-Systeme umfassend produktionstheoretisch fundiert und mittels der allgemeinen Systemtheorie strukturiert beschrieben werden können.