| 1. |
- Bondesson, Lennart, 1944-, et al.
(författare)
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Pareto sampling versus Sampford and Conditional Poisson sampling
- 2006
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Ingår i: Scandinavian Journal of Statistics. - : Wiley InterScience. - 0303-6898 .- 1467-9469. ; 33:4, s. 699-720
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Tidskriftsartikel (refereegranskat)abstract
- Pareto sampling was introduced by Rosén in the late 1990s. It is a simple method to get a fixed size πps sample though with inclusion probabilities only approximately as desired. Sampford sampling, introduced by Sampford in 1967, gives the desired inclusion probabilities but it may take time to generate a sample. Using probability functions and Laplace approximations, we show that from a probabilistic point of view these two designs are very close to each other and asymptotically identical. A Sampford sample can rapidly be generated in all situations by letting a Pareto sample pass an acceptance–rejection filter. A new very efficient method to generate conditional Poisson (CP) samples appears as a byproduct. Further, it is shown how the inclusion probabilities of all orders for the Pareto design can be calculated from those of the CP design. A new explicit very accurate approximation of the second-order inclusion probabilities, valid for several designs, is presented and applied to get single sum type variance estimates of the Horvitz–Thompson estimator.
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| 2. |
- Li, Dai-Qing, et al.
(författare)
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Suppression of sulfonylurea- and glucose-induced insulin secretion in vitro and in vivo in mice lacking the chloride transport protein ClC-3.
- 2009
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Ingår i: Cell metabolism. - : Elsevier BV. - 1932-7420 .- 1550-4131. ; 10:4, s. 309-15
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Tidskriftsartikel (refereegranskat)abstract
- Priming of insulin secretory granules for release requires intragranular acidification and depends on vesicular Cl(-)-fluxes, but the identity of the chloride transporter/ion channel involved is unknown. We tested the hypothesis that the chloride transport protein ClC-3 fulfills these actions in pancreatic beta cells. In ClC-3(-/-) mice, insulin secretion evoked by membrane depolarization (high extracellular K(+), sulfonylureas), or glucose was >60% reduced compared to WT animals. This effect was mirrored by a approximately 80% reduction in depolarization-evoked beta cell exocytosis (monitored as increases in cell capacitance) in single ClC-3(-/-) beta cells, as well as a 44% reduction in proton transport across the granule membrane. ClC-3 expression in the insulin granule was demonstrated by immunoblotting, immunostaining, and negative immuno-EM in a high-purification fraction of large dense-core vesicles (LDCVs) obtained by phogrin-EGFP labeling. The data establish the importance of granular Cl(-) fluxes in granule priming and provide direct evidence for the involvement of ClC-3 in the process.
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| 3. |
- Lundquist, Anders, 1978-
(författare)
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Contributions to the theory of unequal probability sampling
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis consists of five papers related to the theory of unequal probability sampling from a finite population. Generally, it is assumed that we wish to make modelassisted inference, i.e. the inclusion probability for each unit in the population is prescribed before the sample is selected. The sample is then selected using some random mechanism, the sampling design. Mostly, the thesis is focused on three particular unequal probability sampling designs, the conditional Poisson (CP-) design, the Sampford design, and the Pareto design. They have different advantages and drawbacks: The CP design is a maximum entropy design but it is difficult to determine sampling parameters which yield prescribed inclusion probabilities, the Sampford design yields prescribed inclusion probabilities but may be hard to sample from, and the Pareto design makes sample selection very easy but it is very difficult to determine sampling parameters which yield prescribed inclusion probabilities. These three designs are compared probabilistically, and found to be close to each other under certain conditions. In particular the Sampford and Pareto designs are probabilistically close to each other. Some effort is devoted to analytically adjusting the CP and Pareto designs so that they yield inclusion probabilities close to the prescribed ones. The result of the adjustments are in general very good. Some iterative procedures are suggested to improve the results even further. Further, balanced unequal probability sampling is considered. In this kind of sampling, samples are given a positive probability of selection only if they satisfy some balancing conditions. The balancing conditions are given by information from auxiliary variables. Most of the attention is devoted to a slightly less general but practically important case. Also in this case the inclusion probabilities are prescribed in advance, making the choice of sampling parameters important. A complication which arises in the context of choosing sampling parameters is that certain probability distributions need to be calculated, and exact calculation turns out to be practically impossible, except for very small cases. It is proposed that Markov Chain Monte Carlo (MCMC) methods are used for obtaining approximations to the relevant probability distributions, and also for sample selection. In general, MCMC methods for sample selection does not occur very frequently in the sampling literature today, making it a fairly novel idea.
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| 4. |
- Lundquist, Anders, 1978-, et al.
(författare)
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On sampling with desired inclusion probabilities of first and second order
- 2005
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We present a new simple approximation of target probabilities pi for conditional Poisson sampling to obtain given inclusion probabilities. This approximation is based on the fact that the Sampford design gives inclusion probabilities as desired. Some alternative routines to calculate exact pi-values are presented and compared numerically. Further we derive two methods for achieving prescribed 2nd order inclusion probabilities. First we use a probability function belonging to the exponential family. The parameters of this probability function are determined by using an iterative proportional fitting algorithm. Then we modify the conditional Poisson probability function with an additional quadratic factor.
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| 5. |
- Lundquist, Anders, 1978-
(författare)
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On the distance between some πps sampling designs
- 2007
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Ingår i: Acta Applicandae Mathematicae - An International Survey Journal on Applying Mathematics and Mathematical Applications. - Dordrecht : Reidel. - 0167-8019 .- 1572-9036. ; 97:1-3, s. 79-97
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Tidskriftsartikel (refereegranskat)abstract
- Asymptotic distances between probability distributions appearing in πps sampling theory are studied. The distributions are Poisson, Conditional Poisson (CP), Sampford, Pareto, Adjusted CP and Adjusted Pareto sampling. We start with the Kullback-Leibler divergence and the Hellinger distance and derive a simpler distance measure using a Taylor expansion of order two. This measure is evaluated first theoretically and then numerically, using small populations. The numerical examples are also illustrated using a multidimensional scaling technique called principal coordinate analysis (PCO). It turns out that Adjusted CP, Sampford, and adjusted Pareto are quite close to each other. Pareto is a bit further away from these, then comes CP and finally Poisson which is rather far from all the others.
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