title: A comparison of methods for estimating prediction intervals in NIR spectroscopy: Size matters

authors: Bouckaert, Remco R.

subjects: NIR

abstract: In this article we demonstrate that, when evaluating a method for determining prediction intervals, interval size matters more than coverage because the latter can be fixed at a chosen confidence level with good reliability. To achieve the desired coverage, we employ a simple non-parametric method to compute prediction intervals by calibrating estimated prediction errors, and we extend the basic method with a continuum correction to deal with small data sets. In our experiments on a collection of several NIR data sets, we evaluate several existing methods of computing prediction intervals for partial least-squares (PLS) regression. Our results show that, when coverage is fixed at a chosen confidence level, and the number of PLS components is selected to minimize squared error of point estimates, interval estimation based on the classic ordinary least-squares method produces the narrowest intervals, outperforming the U-deviation method and linearization, regardless of the confidence level that is chosen.

text: A comparison of methods for estimating prediction intervals in NIR spectroscopy: Size matters In this article we demonstrate that, when evaluating a method for determining prediction intervals, interval size matters more than coverage because the latter can be fixed at a chosen confidence level with good reliability. To achieve the desired coverage, we employ a simple non-parametric method to compute prediction intervals by calibrating estimated prediction errors, and we extend the basic method with a continuum correction to deal with small data sets. In our experiments on a collection of several NIR data sets, we evaluate several existing methods of computing prediction intervals for partial least-squares (PLS) regression. Our results show that, when coverage is fixed at a chosen confidence level, and the number of PLS components is selected to minimize squared error of point estimates, interval estimation based on the classic ordinary least-squares method produces the narrowest intervals, outperforming the U-deviation method and linearization, regardless of the confidence level that is chosen.

year: 2011

title: The evolution of productivity performance on China's dairy farms in the new millennium

authors: Ma, Hengyun

subjects: China

abstract: China's dairy farm structure has experienced fundamental changes across farm types. As the number of backyard farms has dramatically declined, the share of dairy cows from backyard farms has decreased by 22.4% from 2003 to 2008. However, the herd numbers of larger dairy farms have increased. In particular, the share of dairy cows has risen by 18.8% on small farms, by 22.2% on medium farms, and by 80.8% on large farms over the same period. Total factor productivity was decomposed into technical efficiency and technological change on China's dairy farms using the stochastic production frontier framework. The estimated results indicate that patterns of productivity growth appear to have shifted in the 2000s compared with the 1990s, from generally driven by technological change to exclusively driven by technological change on backyard and small farms and uniquely driven by the improvement of technical efficiency on large farms. Tests of the econometric assumption indicate that the variations in total factor productivity growth patterns across farm types and regions are likely caused by the feed input biases and cropping production practice.

text: The evolution of productivity performance on China's dairy farms in the new millennium China's dairy farm structure has experienced fundamental changes across farm types. As the number of backyard farms has dramatically declined, the share of dairy cows from backyard farms has decreased by 22.4% from 2003 to 2008. However, the herd numbers of larger dairy farms have increased. In particular, the share of dairy cows has risen by 18.8% on small farms, by 22.2% on medium farms, and by 80.8% on large farms over the same period. Total factor productivity was decomposed into technical efficiency and technological change on China's dairy farms using the stochastic production frontier framework. The estimated results indicate that patterns of productivity growth appear to have shifted in the 2000s compared with the 1990s, from generally driven by technological change to exclusively driven by technological change on backyard and small farms and uniquely driven by the improvement of technical efficiency on large farms. Tests of the econometric assumption indicate that the variations in total factor productivity growth patterns across farm types and regions are likely caused by the feed input biases and cropping production practice.

year: 2012

title: A cohort history of mortality in New Zealand

authors: Pool, Ian

abstract: This paper uses the generational life tables to track historical mortality experience for New Zealand Pakeha and Māori. The key research questions we seek to explore concern with why was Pakeha life expectation so high so early, and why did this survival advantage disappeared by the mid 20th century and what has happened since? For the Māori population what was the impact of contact on Māori mortality, what were the changes that have occurred and why, and what has happened to Māori mortality recently? A key finding from the cohort mortality analysis is that gains in survivorship have momentum effects that propel this advantage forward as survivors move up through the age-groups. That said, however, periods of gain may be followed later by cohort deterioration occurring among the same generations later in their life cycle, and even by further cycles of reprise and deterioration. These cycles of gain, deterioration, reprise etc are more evident for males, and particularly for Māori. Policy implications of these findings are discussed.

text: A cohort history of mortality in New Zealand This paper uses the generational life tables to track historical mortality experience for New Zealand Pakeha and Māori. The key research questions we seek to explore concern with why was Pakeha life expectation so high so early, and why did this survival advantage disappeared by the mid 20th century and what has happened since? For the Māori population what was the impact of contact on Māori mortality, what were the changes that have occurred and why, and what has happened to Māori mortality recently? A key finding from the cohort mortality analysis is that gains in survivorship have momentum effects that propel this advantage forward as survivors move up through the age-groups. That said, however, periods of gain may be followed later by cohort deterioration occurring among the same generations later in their life cycle, and even by further cycles of reprise and deterioration. These cycles of gain, deterioration, reprise etc are more evident for males, and particularly for Māori. Policy implications of these findings are discussed.

year: 2003