Conditional Spectral Analysis of Replicated Multiple Time Series with Application to Nocturnal Physiology

This article considers the problem of analyzing associations between power spectra of multiple time series and cross-sectional outcomes when data are observed from multiple subjects. The motivating application comes from sleep medicine, where researchers are able to non-invasively record physiological time series signals during sleep. The frequency patterns of these signals, which can be quantified through the power spectrum, contain interpretable information about biological processes. An important problem in sleep research is drawing connections between power spectra of time series signals and clinical characteristics; these connections are key to understanding biological pathways through which sleep affects, and can be treated to improve, health. Such analyses are challenging as they must overcome the complicated structure of a power spectrum from multiple time series as a complex positive-definite matrix-valued function. This article proposes a new approach to such analyses based on a tensor-product spline model of Cholesky components of outcome-dependent power spectra. The approach flexibly models power spectra as nonparametric functions of frequency and outcome while preserving geometric constraints. Formulated in a fully Bayesian framework, a Whittle likelihood based Markov chain Monte Carlo (MCMC) algorithm is developed for automated model fitting and for conducting inference on associations between outcomes and spectral measures. The method is used to analyze data from a study of sleep in older adults and uncovers new insights into how stress and arousal are connected to the amount of time one spends in bed

Linkage between World and Domestic Prices of Rice under the regime of Agricultural Trade Liberalization in Bangladesh

The paper examines the relationship between the world market and domestic market prices of rice for Bangladesh in the regime of agricultural trade liberalization. The long run price relationship information is an important piece of information for the policy makers in formulating domestic polices and negotiating trade policies at the international level. The monthly data used for this study are taken from different sources, the Food outlook, FAO and Global Information and Early Warning System, FAO and the Bangladesh Bank for the period June 1998 to July 2007. Both Engle-Granger bi-variate and Johansen multivariate cointegration tests were used for the results sensitivity. We sequentially proceed to estimate the standard error correction model. The results showed that there is a long run equilibrium relationship between the world and the domestic prices and the relationship is uni-directional, meaning that, the domestic prices adjust to the world prices but not vice-versa. So the policy to ensure food security (via food price stability and price risk management) should be carefully designed as the movement of the world market price is higher and distorted and many consumers depend on the markets for their food, especially in the case of Bangladesh.Market integration, Domestic price, World price, Error correction model, Marketing,

Surf zone hyperbenthos of Belgian sandy beaches: seasonal patterns

Since surf zone hyperbenthos, although highly important in local food webs, has often been neglected and very little information is available, a survey of the Belgian sandy beaches was carried out from May 1996 until July 1997. Monthly samples were taken to give a complete record of hyperbenthic organisms occurring in the surf zone of Belgian sandy beaches and to evaluate the intensity by which this surf zone is used. In total 172 species were recorded. The number of species occurring in the surf zone is comparable to that of adjacent areas. As weIl as true hyperbenthic species, endobenthic and planktonic organisms were sampled. More than 75% of the average total sample composition consisted of mysids, mainly Mesopodopsis slabberi, Schistomysis spiritus and Schistomysis kervillei (holohyperbenthos). Apart from several resident species, active and passive seasonal migration towards the surf zone by a number of species is suggested. A large number of sporadic species adds to the composition of surf zone hyperbenthos. Within the merohyperbenthos, postlarval decapods and fish were the dominant organisms. During the year three recruitment peaks were observed. Average densities per month exceeded 1500 ind. 100 m-2. Yearly biomass averages ranged from 300 to over 3000 mg ADW 100 m-2. Densities of the common species are slightly higher in the surf zone than in other habitats, emphasising the importance of the area. Besides a possible nursery function, the surf zone may also be used as a transient area between different habitats. Finally, the influence of several abiotic factors on the hyperbenthic assemblages was evaluated. The main structuring variables determining the occurrence of most of the organisms are water temperature and hydrodynamic factors such as wave height and turbidity. The influence of wave height seems to be two-fold: several good swimmers such as mysids and some fish species are suggested to be able to actively avoid severe wave conditions, whereas other, more planktonic organisms, are passively transported towards the area if wave height increases

Testing Asymmetric Price Transmission in the Vertical Supply Chain in De-regulated Rice Markets in Bangladesh

Market liberalization at the domestic level and at the boarder level has been a dominant feature of market reforms in most developing countries including Bangladesh during the last two decades. A pre-requisite for producers and consumers to benefit from this new and changing market environment is the ability of market to function efficiently at their spatial or through the value chain dimensions which are very often constrained by different factors. The vertical integration of grain markets plays a crucial role in improving the welfare of the producers and the consumers. Therefore, the better the market integration, the lesser the intervention required by the government. There was a widely-held belief about the domestic markets in Bangladesh on possible manipulation in the agricultural markets as well as concerns about the sources of asymmetry. In the domestic markets, a price increase passes very quickly though the supply chain compared to a price decrease. As a result, perception by consumers and the government exists that at least the market is being manipulated, raising food prices unfairly, at the expenses of the poor households who are net buyers and for whom food is a major expenditure share (about 40-50 percent). Examining, the market functioning at the vertical level in developing countries is of importance to evaluate how the private traders delivering to the market. That is why it is important to identify what kind of policy can be introduced and at what level of the marketing chain to correct the market inefficiency, if needed. The vertical price leadership at the wholesale level to the retail in the marketing literature is inferred but not empirically verified. Therefore, this paper is an attempt to fill up this gap. It first examines the price transmission between the wholesale and retail level of the rice market in Bangladesh in the regime of the changing market environment. Secondly, it examines whether the wholesale market dominates the retail one. Thirdly, it analyzes whether the price relationship is symmetric with respect to price increases and price decreases. The paper uses the average wholesale and retail price of rice for Bangladesh. The monthly price data used for this study are taken from FAO and different published series of Statistical Yearbook and the Economic Trend. The data period cover from February 2002 to June, 2007. From our unit root test, we find that the level data contain one unit root but are stationary at their first differences. Both Engel-Granger (1987) bi-variate and Johansen (1990)multivariate cointegration tests were applied to determine a linear combination which is stationary. Then the existence of long run causality was tested within the framework of Johansen cointegration by standard Wald test. To test the asymmetric transmission in the prices we used the asymmetric ECM-EG approach. The results show that the wholesale and retail prices are integrated, and in the line of the industrial organization theory, the wholesale price plays a leadership role to determine the retail prices. Results also confirm that the consumer and public concern about the asymmetric price transmission holds true.agricultural economics, agricultural marketing, Agribusiness, Agricultural and Food Policy, Demand and Price Analysis, Marketing,

Tracing the impact of market reform on productivity growth of rice at the farm level in Bangladesh

The paper measures the total factor productivity (TFP), technical change (TC) and technical efficiency change (TEC) in rice production, and traces the impact of market reform policies of the 1990s on these indices at the farm level in Bangladesh using a unique cohort of three-period panel data (1987, 2000 and 2004) of 73 farms by applying stochastic production frontier approach. Results reveal that the TFP index has increased by 27% largely due to an upward shift of the technology frontier. Although TC has increased by an impressive 57%, TEC declined by 30.1% during the post-reform period, thereby depressing overall TFP growth. The market liberalization policies exerted significantly positive impacts on TC and TFP growth but negatively on TEC. Farm size and household size also significantly improved these indices while education, tenancy and off-farm income exerted negative effects. Policy implications include continued liberalization of markets and land reform measures to increase farm size