This paper considers a stochastic frontier production function which has additive, heteroscedastic error structure. The model allows for negative or positive marginal production risks of inputs, as originally proposed by Just and Pope (1978). The technical efficiencies of individual firms in the sample are a function of the levels of the input variables in the stochastic frontier, in addition to the technical inefficiency effects. These are two features of the model which are not exhibited by the commonly used stochastic frontiers with multiplicative error structures.An empirical application is presented using cross-sectional data on Ethiopian peasant farmers. The null hypothesis of no technical inefficiencies of production among these farmers is accepted. Further, the flexible risk models do not fit the data on peasant farmers as well as the traditional stochastic frontier model with multiplicative error structure. 相似文献
Background: Validation of overall survival (OS) extrapolations of immune-checkpoint inhibitors (ICIs) during the National Institute for Health and Care Excellence (NICE) Single Technology Assessment (STA) process is limited due to data still maturing at the time of submission. Inaccurate extrapolation may lead to inappropriate decision-making. The availability of more mature trial data facilitates a retrospective analysis of the plausibility and validity of initial extrapolations. This study compares these extrapolations to subsequently available longer-term data.
Methods: A systematic search of completed NICE appraisals of ICIs from March 2000 to December 2017 was performed. A targeted search was also undertaken to procure published OS data from the pivotal clinical trials for each identified STA made available post-submission to NICE. Initial Kaplan-Meier curves and associated extrapolations from NICE documentation were extracted to compare the accuracy of OS projections versus the most mature data.
Results: The review identified 11 STAs, of which 10 provided OS data upon submission to NICE. The extrapolations undertaken considered parametric or piecewise survival models. Additional data cut-offs provided a mean of 18 months of OS beyond the end of the original data. Initial extrapolations typically under-estimated OS from the most mature data cut-off by 0.4–2.7%, depending on the choice of assessment method and use of the manufacturer- or ERG-preferred extrapolation.
Conclusion: Long-term extrapolation of OS is required for NICE STAs based on initial immature OS data. The results of this study demonstrate that the initial OS extrapolations employed by manufacturers and ERGs generally predicted OS reasonably well when compared to more mature data (when available), although on average they appeared to underestimate OS. This review and validation shows that, while the choice of OS extrapolation is uncertain, the methods adopted are generally aligned with later-published follow-up data and appear appropriate for informing HTA decisions. 相似文献
This paper applies the principles of the neo-Ricardian (or Sraffian)theory of international trade to certain joint production systems.It is shown that, in contrast with single-product systems, (i)there is not always a pattern of international specialisation,which would entail the increase of the real wage rate in botheconomies, and (ii) the law of comparative advantagehas no general validity. Furthermore, not only the existenceof such a pattern of specialisation but also the validity ofthis law depend on the values of the variables of distributionof income. The analysis is wholly based on two of the numericalexamples formulated by Bidard in 1997, and further generalisedin an elementary way only when this is considered necessary. 相似文献
To meet the sustainability challenge private companies must implement corporate strategies and adopt novel technologies. The technical and social embeddedness of industrial production systems, however, complicates these systems' transition towards sustainability. In the paper, mechanisms and conditions are reported for the development and implementation of waste management options in embedded industrial production systems. The focus is on the Dutch zinc production industry, which had to deal with a major waste problem; the generation of jarosite. The industry's options were to increase the jarosite waste storage capacity, to develop a jarosite treatment process or to switch to a zinc-ore of low-iron content whereby no jarosite waste would be generated anymore. Required conditions appeared to be a combination of technological capability and technical embedding and favourable economics. Case study research, however, revealed that adequate stakeholder management is crucial to address social pressure exerted and to obtain external acceptance for any transition strategy. Whilst appropriate, internal technological capabilities are important, effective interactions with and enrolment of various firm-external actors are crucial. In the case of zinc, access to the heterogeneous external actor network was critical for the development of the jarosite treatment solution direction. In conclusion, both the technical, organizational and social embedding of new technologies are crucial for successful implementation. 相似文献