A Nonlinear Unit Root Test in the Presence of an Unknown Break

The Perron test is the most commonly applied procedure to test for a unit root in the presence of a structural break of unknown timing in the trend function. Deriving the Perron-type test regression from an unobserved component model, it is shown that the test regression in fact is nonlinear in coefficient. Taking account of the nonlinearity leads to a test with properties that are exclusively assigned to Schmidt-Phillips LM-type unit root tests.Unit root tests, nonlinear regression, structural breaks, innovational outliers

Identification of the true break date in innovational outlier unit root tests

The present paper considers Dickey-Fuller-type unit root tests which account for a structural break occurring at an unknown point in time. The break is modelled by an innovational outlier approach. Provided that the break date is estimated correctly, the exact invariance to a mean and a slope shift holds for these tests under the null hypothesis. An erroneous estimation of the break date leads to considerable spurious rejections of the null hypothesis in small samples. In this paper, test procedures are developed using a components representation of the data generating process. In contrast to the conventionally used approaches, these tests enable the identification of the true break date and ensure the invariance property of the corresponding test statistics. Monte Carlo simulations of size and power testify the favorable properties of the developed tests. --Unit root tests,structural break,endogenous break date estimation,innovational outlier models,spurious rejections,component representation

Identification of the true break date in innovational outlier unit root tests

The present paper considers Dickey-Fuller-type unit root tests which account for a structural break occurring at an unknown point in time. The break is modelled by an innovational outlier approach. Provided that the break date is estimated correctly, the exact invariance to a mean and a slope shift holds for these tests under the null hypothesis. An erroneous estimation of the break date leads to considerable spurious rejections of the null hypothesis in small samples. In this paper, test procedures are developed using a components representation of the data generating process. In contrast to the conventionally used approaches, these tests enable the identification of the true break date and ensure the invariance property of the corresponding test statistics. Monte Carlo simulations of size and power testify the favorable properties of the developed tests

A Panel-CADF Test for Unit Roots

In this paper we propose the extension of the covariate-augmented Dickey Fuller (CADF) test for unit roots developed by Hansen (1995} to the panel case. We show that the extension is viable and gives power gains with respect to the time series approach. Particular attention is paid to cross-unit dependence.Unit root, Panel data, Cross-unit dependence

Land management and ecosystem services. How collaborative research programmes can support better policies

Land management, the organisation of the use and development of land, is an important instrument for addressing problems of rising greenhouse gas emissions and loss of natural resources. Yet, natural-social systems in which land management policies are implemented are poorly understood, thus decreasing the effectiveness of these policies. Local studies provide valuable insights, though only for the local conditions prevalent during the investigated period. Synthesising local studies in order to generalise results is impaired by the variety of local conditions. Collaborative research programmes may prevent some of these problems. They support the share of insights across temporal, ecological and spatial-economic contexts. On the basis of existing literature, we identify the challenges which face synthesis and demonstrate how a German research programme attempts to address some of them

A Panel-CADF Test for Unit Roots

In this paper we propose the extension of the covariate-augmented Dickey Fuller (CADF) test for unit roots developed by Hansen (1995} to the panel case. We show that the extension is viable and gives power gains with respect to the time series approach. Particular attention is paid to cross-unit [email protected]@[email protected]

Different response to eccentric and concentric training in older men and women

Sarcopenia is the age-related loss of muscle mass and strength and has been associated with an increased risk of falling and the development of metabolic diseases. Various training protocols, nutritional and hormonal interventions have been proposed to prevent sarcopenia. This study explores the potential of continuous eccentric exercise to retard age-related loss of muscle mass and function. Elderly men and women (80.6±3.5years) were randomized to one of three training interventions demanding a training effort of two sessions weekly for 12weeks: cognitive training (CT; n=16), conventional resistance training (RET; n=23) and eccentric ergometer training (EET; n=23). Subjects were tested for functional parameters and body composition. Biopsies were collected from M. vastus lateralis before and after the intervention for the assessment of fiber size and composition. Maximal isometric leg extension strength (MEL: +8.4±1.7%) and eccentric muscle coordination (COORD: −43±4%) were significantly improved with EET but not with RET (MEL: +2.3±2.0%; COORD: −13±3%) and CT (MEL: −2.3±2.5%; COORD: −12±5%), respectively. We observed a loss of body fat (−5.0±1.1%) and thigh fat (−6.9±1.5%) in EET subjects only. Relative thigh lean mass increased with EET (+2.5±0.6%) and RET (+2.0±0.3%) and correlated negatively with type IIX/type II muscle fiber ratios. It was concluded that both RET and EET are beneficial for the elderly with regard to muscle functional and structural improvements but differ in their spectrum of effects. A training frequency of only two sessions per week seems to be the lower limit for a training stimulus to reveal measurable benefit

Biologically relevant sex differences for fitness-related parameters in active octogenarians

The number of elderly people is growing in western populations, but only few maximal performance data exist for people >75years, in particular for European octogenarians. This study was performed to characterize maximal performance of 55 independently living subjects (32 women, 81.1±3.4years; 23 men, 81.7±2.9years) with a focus on sex differences. Maximal performance was determined in a ramp test to exhaustion on a bicycle ergometer with ergospirometry, electrocardiogram and blood lactate measurements. Maximal isometric extension strength of the legs (MEL) was measured on a force platform in a seated position. Body composition was quantified by X-ray absorptiometry. In >25% of the subjects, serious cardiac abnormalities were detected during the ramp test with men more frequently being affected than women. Maximal oxygen consumption and power output were 18.2±3.2 versus 25.9±5.9mlmin−1kg−1 and 66±12 versus 138±40W for women versus men, with a significant sex difference for both parameters. Men outperformed women for MEL with 19.0±3.8 versus 13.6±3.3Nkg−1. Concomitantly, we found a higher proportion of whole body fat in women (32.1±6.2%) compared to men (20.5±4.4%). Our study extends previously available maximal performance data for endurance and strength to independently living European octogenarians. As all sex-related differences were still apparent after normalization to lean body mass, it is concluded that it is essential to differentiate between female and male subjects when considering maximal performance parameters in the oldest segment of our populatio