BIG sampling

Graph sampling is a statistical approach to study real graphs, which represent the structure of many technological, social or biological phenomena of interest. We develop bipartite incident graph sampling (BIGS) as a feasible representation of graph sampling from arbitrary finite graphs. It provides also a unified treatment of the existing unconventional sampling methods which were studied separately in the past, including indirect, network and adaptive cluster sampling. The sufficient and necessary conditions of feasible BIGS representation are established, given which one can apply a family of Hansen-Hurwitz type design-unbiased estimators in addition to the standard Horvitz-Thompson estimator. The approach increases therefore the potentials of efficiency gains in graph sampling. A general result regarding the relative efficiency of the two types of estimators is obtained. Numerical examples are given to illustrate the versatility of the proposed approach

Empirical likelihood confidence intervals and significance test for regression parameters under complex sampling designs

Confidence intervals based on ordinary least squares may have poor coverages for regression parameters when the effect of sampling design is ignored. Standard confidence intervals based on design variances may not have the right coverages when the sampling distribution is skewed. Berger and De La Riva Torres (2012) proposed an empirical likelihood approach which can be used for point estimation and to construct confidence intervals under complex sampling designs for a single parameter. We show that this approach can be extended to test the significance of a subset of model parameters and to derive confidence intervals. The proposed approach is not a straightforward extension of Berger and De La Riva Torres (2012) approach, because we consider the situation when the parameter is multidimensional and the parameter of interest is a subset of the parameter. This requires profiling which is not covered by Berger and De La Riva Torres (2012). The proposed approach intrinsically incorporates sampling weights, design variables, and auxiliary information. It may yield to more accurate confidence intervals when the sampling distribution of the regression parameters is not normal, the point estimator is biased, or the regression model is not linear. The proposed approach is simple to implement and less computer intensive than bootstrap. The proposed approach does not rely on re-sampling, linearisation, variance estimation, or design-effect

Teknisk rapport for pilotundersøkelsen av forsøpling i Kristiansand kommune

Søppelundersøkelser har blitt gjennomført i Sverige i rundt ti år i samarbeid med Hold Sverige Rent (HSR), Statistiska centralbyrå (SCB) og svenske kommuner. I 2017 ble det planlagt å gjennomføre en slik undersøkelse i Norge under ledelse av Hold Norge Rent (HNR) for å kartlegge forsøpling i norske kommuner. Målet med å gjennomføre en slik undersøkelse er å overvåke forekomsten av søppel for deretter å gjøre nødvendige tiltak mot forsøpling. Det ble bestemt at en pilotundersøkelse skulle gjennomføres i Kristiansand kommune. Målet med pilotundersøkelsen var å finne ut hvordan man kan kartlegge mengden av søppel i norske kommuner. Den svenske metoden ble brukt uten noen endringer, bortsett fra stratifiseringen av utvalgsområdene. Områdene som måles kan deles inn i to grupper: i) gateområder og ii) parker og grønne områder. Gravaneparken og en fjerdedel av Kvadraturen i Kristiansand ble valgt som målområder for henholdsvis park- og gatemålinger. Målet var å gi estimater for mengde søppel av ulike typer per ti kvadratmeter. Utvalgsramme, utvalgsenhet, spørreskjema og måten å samle inn data på er forskjellig for de to områdene. Denne rapporten gir en oversikt over hele metodologien som ble brukt i pilotundersøkelsen, samt hensyn og anbefalinger angående ulike deler av metodikken. Undersøkelsesresultater angående de valgte områdene presenteres også. Man må imidlertid være klar over at dette er basert på en begrenset mengde data. Derfor kan de statistiske tallene ha stor usikkerhet.publishedVersio

Simultaneous use of Individual and Joint Regularization Terms in Compressive Sensing: Joint Reconstruction of Multi-Channel Multi-Contrast MRI Acquisitions

Purpose: A time-efficient strategy to acquire high-quality multi-contrast images is to reconstruct undersampled data with joint regularization terms that leverage common information across contrasts. However, these terms can cause leakage of uncommon features among contrasts, compromising diagnostic utility. The goal of this study is to develop a compressive sensing method for multi-channel multi-contrast magnetic resonance imaging (MRI) that optimally utilizes shared information while preventing feature leakage. Theory: Joint regularization terms group sparsity and colour total variation are used to exploit common features across images while individual sparsity and total variation are also used to prevent leakage of distinct features across contrasts. The multi-channel multi-contrast reconstruction problem is solved via a fast algorithm based on Alternating Direction Method of Multipliers. Methods: The proposed method is compared against using only individual and only joint regularization terms in reconstruction. Comparisons were performed on single-channel simulated and multi-channel in-vivo datasets in terms of reconstruction quality and neuroradiologist reader scores. Results: The proposed method demonstrates rapid convergence and improved image quality for both simulated and in-vivo datasets. Furthermore, while reconstructions that solely use joint regularization terms are prone to leakage-of-features, the proposed method reliably avoids leakage via simultaneous use of joint and individual terms. Conclusion: The proposed compressive sensing method performs fast reconstruction of multi-channel multi-contrast MRI data with improved image quality. It offers reliability against feature leakage in joint reconstructions, thereby holding great promise for clinical use.Comment: 13 pages, 13 figures. Submitted for possible publicatio

PROCJENA NADZEMNE BIOMASE UGLJIKA KORIŠTENJEM VRIJEDNOSTI REFLEKSIJE SATELITSKIH SNIMAKA: STUDIJA SLUČAJA U DIREKCIJI ŠUMA, CAMYAZI, TURSKA

Forest ecosystems which contain half of the terrestrial carbon deposits; play a significant role in shaping the global climate. Two different methods are used to determine the above-ground carbon stock capacity of forestlands. Direct measurement method takes a long time and requires both extensive as well as expensive field and laboratory work. One of the more indirect methods, satellite imaging on the other hand, costs less, is easier and practical compared to direct methods. It is also easier to integrate into geographic information systems (GIS). This paper provides a regression equation between the reflection values from RapidEye high resolution satellite image and sample areas where terrestrial aboveground biomass (AGB) carbon stock capacity was calculated by direct measurement method. As a result of the calculations made, using the RapidEye imagery and a “Band 4” devised equation producing R2=0.71 depending upon the data from Erzurum Camyazi Forest Directorate encompassing 9,917 ha study area, the amount of carbon stored within stands was found 285 208 tons. From this value, we can conclude that average carbon stock of the study area is 28.8 tons/ha.Postoje tri glavna nalazišta ugljika na svijetu. To su atmosfera, zemaljski i oceanski ekosustavi. Šume su najveće zemaljsko nalazište ugljika. Postoji linearni odnos između količine šumskih područja i pohranjenog ugljika. Također, u kontekstu Kyoto protokola, šumska zemljišta i količina pohranjenog ugljika jako su važni za razmjenu ugljika u nadolazećim godinama. Svrha ovog istraživanja je formalizirati jednadžbu regresije između kapaciteta pohrane nadzemnog ugljika izračunatog kroz ekstenzivni terenski pregled 344 područja uzoraka u Direkciji šuma Camyazi, Turska, te vrijednosti refleksije koje odgovaraju svakom uzorku od slika RapidEye. U istraživanju su se koristili inventarni podaci plana gospodarenja te tehnike daljinskog istraživanja za utvrđivanje količine ugljika pohranjene u sastojini unutar granica Direkcije šuma Camyazi, Turska. Kao rezultat izvršenih kalkulacija, korištenjem slika RapidEye te (Pojas 4)2 izvedene jednadžbe koja daje R2=0.71, ovisno o podacima Direkcije šuma Erzurum Camyazi, utvrđeno je da je količina ugljika pohranjena u sastojini iznosila 285 208 tona. Iz te vrijednosti možemo zaključiti da je prosječna pohrana ugljika u ispitivanom području 28.8 tona/ha. Tehnike daljinskog istraživanja korištene u ovome istraživanju pokazale su da te tehnike mogu uštedjeti vrijeme, financijska sredstva i posao kod izračuna podataka kapaciteta pohrane ugljika (koje zahtijeva prilično vremena i sredstava za izračun), a mogu se dobiti precizni rezultati. Uz to, istraživanje je pokazalo da je Red-Edge pojas (Pojas 4) satelitske slike RapidEye-a osjetljiv na biomasu i klorofil se može koristiti u istraživanjima povezanim s pohranom ugljika. Jednadžbe za biomasu i pohranu ugljika za svaku vrstu šumskog drveća još nisu dovršene. Trebaju se dovršiti što je prije moguće i kapacitet pohrane ugljika treba se točnije utvrditi. Kod izračuna kapaciteta za ovaj tip istraživanja treba uzeti u obzir financijsku stranu istraživanja uz preferiranje kombinirane metode s niskim troškovima

Coal Consumption and Economic Growth in Turkey

This aim of this paper is to use asymmetric causality tests to examine the coal consumption and Gross Domestic Product (GDP) relationship in Turkey based on data from 1980 to 2006. To investigate this relationship, a multivariate system is employed by including fixed capital formation and labor force variables into the model. The empirical results obtained from asymmetric causality tests show no causality for coal consumption and GDP relationship in Turkey. The results indicate that coal consumption does not affect growth; hence, energy conservation policies may be pursued without adversely affecting growth in Turkey. Thus, neutrality hypothesis is confirmed for Turkey. This means that a decrease in coal consumption does not affect economic growth and vice versa. In this case, policymakers should explore the feasibility of either decreasing the coal consumption or increasing the efficiency of coal consumption. Keywords: Economic growth; coal consumption; asymmetric causality; Turkey JEL Classifications: O; Q4

A simple variance estimator of change for rotating repeated surveys: an application to the EU-SILC household surveys

A common problem is to compare two cross-sectional estimates for the same study variable taken on two different waves or occasions, and to judge whether the change observed is statistically significant. This involves the estimation of the sampling variance of the estimator of change. The estimation of this variance would be relatively straightforward if cross-sectional estimates were based on the same sample. Unfortunately, samples are not completely overlapping, because of rotations used in repeated surveys. We propose a simple approach based on a multivariate (general) linear regression model. The variance estimator proposed is not a model-based estimator. We show that the estimator proposed is design consistent when the sampling fractions are negligible. It can accommodate stratified and two-stage sampling designs. The main advantage of the approach proposed is its simplicity and flexibility. It can be applied to a wide class of sampling designs and can be implemented with standard statistical regression techniques. Because of its flexibility, the approach proposed is well suited for the estimation of variance for the European Union Statistics on Income and Living Conditions surveys. It allows us to use a common approach for variance estimation for the different types of design. The approach proposed is a useful tool, because it involves only modelling skills and requires limited knowledge of survey sampling theory

Hemoglobin is inversely related to flow-mediated dilatation in chronic kidney disease

The microcirculation is regulated by oxygen gradients and by endothelial release of nitric oxide, which can react with hemoglobin to form S-nitroso derivatives. Here we induced flow-mediated dilatation of the brachial artery in response to ischemia in 141 non-diabetic patients with stage 3–4 chronic kidney disease who had no history of smoking, cardiovascular events or use of erythropoietin-based agents. Patients with hemoglobin concentrations above the cohort median of 11.6 g/dl were found to have significant reductions in flow-mediated dilatation compared to those below the median. This inverse relationship remained significant after adjustment for potential confounders, including insulin sensitivity, glomerular filtration rate, proteinuria, body mass index, serum urate, etiology of underlying renal disease, treatment with anti-hypertensive drugs, and traditional Framingham risk factors. Given that hemoglobin can act as an important nitric oxide carrier and buffer, our studies suggest that the mechanism by which hemoglobin influences the endothelium-dependent microcirculation requires its nitrosylation; however, more direct studies need to be performed

FGF-23 and vascular dysfunction in patients with stage 3 and 4 chronic kidney disease

Studies in animals show that fibroblast growth factor (FGF)-23 interferes with vascular reactivity induced by the nitric oxide (NO) system. To investigate the relationship between circulating FGF-23 levels and the response of forearm blood flow to ischemia (flow-mediated vasodilatation, FMD) and nitroglycerin, we tested 183 patients with stage 3-4 chronic kidney disease (CKD). None of them had cardiovascular complications or were taking drugs interfering with vascular function. Patients with FGF-23 levels above the median had significantly lower glomerular filtration rate, FMD, and fetuin-A levels (an anti-inflammatory molecule and potent inhibitor of calcification). They also had higher proteinuria and phosphate levels when compared to patients whose FGF-23 levels were below the median. The response to nitroglycerin was not different between the two groups. Multiple regression analysis showed that the relationship between FGF-23 and FMD was only modestly sensitive to adjustment for classical risk factors, biomarkers of bone mineral metabolism, high-sensitivity C-reactive protein, and homeostatic model assessment index. Adjustment for asymmetrical dimethyl arginine (ADMA) weakened the strength of this link; however, it remained highly significant. There was no independent association between FGF-23 and nitroglycerin. Thus, attenuation of FMD by ADMA suggests that this endogenous inhibitor of NO synthase may, in part, mediate the vascular effects of FGF-23 in patients with CKD. © 2010 International Society of Nephrology