Search results for "Trend."
showing 10 items of 394 documents
Secular trends in moderate-to-vigorous physical activity in 32 countries from 2002 to 2010: a cross-national perspective
2015
Background: Sufficient levels of moderate to vigorous physical activity (MVPA) give substantial health benefits to adolescents. This article examines trends in physical activity (PA) from 2002 to 2010 across 32 countries from Europe and North America. Methods: Representative samples included 479 674 pupils (49% boys) aged 11 years ( n = 156 383), 13 years ( n = 163 729) and 15 years ( n = 159 562). The trends in meeting the recommendations for PA (at least 60 min daily) were evaluated using logistic regression. Results: There was a slight overall increase between 2002 and 2010 (17.0% and 18.6%, respectively). MVPA increased significantly ( P ≤ 0.05) among boys in 16 countries. Conversely, n…
Convergence in car prices among European countries
2011
This article contributes to the literature on price convergence in Europe by investigating the existence of stochastic and deterministic convergence of car prices in the EU15 countries. We apply recently developed econometric techniques that allow for multiple structural breaks to an up-to-date dataset. We find considerable evidence of both types of convergence in our sample of countries and car models, therefore suggesting a tendency for relative prices to equalize over time. In addition, we find evidence regarding the importance in this convergence process of both legislative changes taking place in the years 1996 and 2002, and the implementation of Economic and Monetary Union (EMU).
La décomposition canonique et la cointégration
1994
This paper has introduced state space models for cointegrated time series. In doing so, the notion of cointegration is slightly generalized. We develop the notion of dynamic aggregation link with error correction model and common trends.
Non-stationarity tests and nonlinear trends
1992
This paper stresses the importance of the hypothesis of linearity of the deterministic component imposed by unit root testing procedures most frequently used in empirical literature. We suggest an empirical testing strategy which reduces the risk of reaching false conclusions due to the misspecification of that component and we apply it to the analysis of the nonstationarity exhibited by real GNP in France. We show that it is possible to find someflexible specifications which enable us to reject the unit root null hypothesis otherwise strongly supported in empirical literature. These specifications might be considered as approximations of the true process generating real GNP and might be us…
Statistical analysis of inter-arrival times of rainfall events for Italian Sub-Alpine and Mediterranean areas
2012
Abstract. In this work a set of time-series of inter-arrival times of rainfall events, at daily scale, was analysed, with the aim to verify the issue of increasing duration of dry periods. The set consists of 12 time-series recorded at rain gauges in 1926–2005, six of them belong to an Italian Sub-Alpine area (Piedmont) and six to a Mediterranean one (Sicily). In order to overcome the problem related to limited sample size for high values of inter-arrival times, the discrete probability polylog-series distribution was used to fit the empirical data from partial (20 yr) time-series. Moreover, a simple qualitative trend analysis was applied to some high quantiles of inter-arrival times as wel…
That twenty years is nothing for gravel-pit limnology
2020
[EN] The past twenty years have witnessed a rise in the analysis of long-term limnological data given the need to know whether global warming is affecting freshwaters, and if so, how. Previous studies indicated that processes affecting ecosystem function-ing may develop slowly, thus requiring long-term study, as in the case of the eutrophication-oligotrophication gradient. Here we report annual averages and seasonal variability of meteorological data (air temperature, solar radiation, rainfall) and the main limnological variables (lake level, water temperature, euphotic depth, mixing depth, nitrogen and phosphorus compounds and phytoplankton biomass) for a gravel-pit, seepage lake close to …
A time series study on the effects of heat on mortality and evaluation of heterogeneity into European and Eastern-Southern Mediterranean cities: resu…
2013
Background: The Mediterranean region is particularly vulnerable to the effect of summer temperature. Within the CIRCE project this time-series study aims to quantify for the first time the effect of summer temperature in Eastern-Southern Mediterranean cities and compared it with European cities around the Mediterranean basin, evaluating city characteristics that explain between-city heterogeneity. Methods: The city-specific effect of maximum apparent temperature (Tappmax) was assessed by Generalized Estimation Equations, assuming a linear threshold model. Then, city-specific estimates were included in a random effect meta-regression analysis to investigate the effect modification by several…
Rainfall statistics changes in Sicily
2013
Abstract. Changes in rainfall characteristics are one of the most relevant signs of current climate alterations. Many studies have demonstrated an increase in rainfall intensity and a reduction of frequency in several areas of the world, including Mediterranean areas. Rainfall characteristics may be crucial for vegetation patterns formation and evolution in Mediterranean ecosystems, with important implications, for example, in vegetation water stress or coexistence and competition dynamics. At the same time, characteristics of extreme rainfall events are fundamental for the estimation of flood peaks and quantiles which can be used in many hydrological applications, such as design of the mos…
Global land surface phenology trends from GIMMS database
2009
A double logistic function has been used to describe global inventory mapping and monitoring studies (GIMMS) normalized difference vegetation index (NDVI) yearly evolution for the 1981 to 2003 period, in order to estimate land surface phenology parameter. A principal component analysis on the resulting time series indicates that the first components explain 36, 53 and 37% of the variance for the start, end and length of growing season, respectively, and shows generally good spatial homogeneity. Mann-Kendall trend tests have been carried out, and trends were estimated by linear regression. Maps of these trends show a global advance in spring dates of 0.38 days per year, a global delay in aut…
Trend following with momentum versus moving averages: a tale of differences
2020
Despite the ever-growing interest in trend following and a series of publications in academic journals, there is a dearth of theoretical results on the properties of trend-following rules. Our pape...