Bias of the Quasi Score Estimator of a Measurement Error Model Under Misspecification of the Regressor Distribution

In a structural error model the structural quasi score (SQS) estimator is based on the distribution of the latent regressor variable. If this distribution is misspecified the SQS estimator is (asymptotically) biased. Two types of misspecification are considered. Both assume that the statistician erroneously adopts a normal distribution as his model for the regressor distribution. In the first type of misspecification the true model consists of a mixture of normal distributions which cluster round a single normal distribution, in the second type the true distribution is a normal distribution admixed with a second normal distribution of low weight. In both cases of misspecification the bias, of course, tends to zero when the size of misspecification tends to zero. However, in the first case the bias goes to zero very fast so that small deviations from the true model lead only to a negligible bias, whereas in the second case the bias is noticeable even for small deviations from the true model

Note on Two Estimators for the Polynomial Regression with Errors in the Variables

This Note generalizes two estimators of the quadratic regression with measurement errors by Fuller and Wolter and Fuller to the polynomial case

On the bias of structural estimation methods in a polynomial regression with measurement error when the distribution of the latent covariate is a mixture of normals

The structural variant of a regression model with measurement error is characterized by the assumption of an underlying known distribution of the latent covariate. Several estimation methods, like regression calibration or structural quasi score estimation, take this distribution into account. In the case of a polynomial regression, which is studied here, structural quasi score takes the form of structural least squares (SLS). Usually the underlying latent distribution is assumed to be the normal distribution because then the estimation methods take a particularly simple form. SLS is consistent as long as this assumption is true. The purpose of the paper is to investigate the amount of bias that results from violations of the normality assumption for the covariate distribution. Deviations from normality are introduced by switching to a mixture of normal distributions. It turns out that the bias reacts only mildly to slight deviations from normality

A Small Sample Estimator for a Polynomial Regression with Errors in the Variables

An adjusted least squares estimator, introduced by Cheng and Schneeweiss (1998) for consistently estimating a polynomial regression of any degree with errors in the variables, is modified such that it shows good results in small samples without losing its asymptotic properties for large samples. Simulation studies corroborate the theoretical findings. The new method is applied to analyse a geophysical law relating the depth of earthquakes to their distance from a trench where one of the earth's plates is submerged beneath another one

Matrix metalloproteinase-3 promoter polymorphisms but not dupA-H. pylori correlate to duodenal ulcers in H. pylori-infected females

<p>Abstract</p> <p>Background</p> <p>This study investigated if the <it>H. pylori dupA </it>genotype and certain host single nucleotide polymorphisms (SNPs) of matrix metalloproteinases (MMPs) and their inhibitors (TIMPs), including MMP-3, MMP-7, MMP-9, TIMP-1 and TIMP-2, might correlate with ulcer risk of <it>H. pylori-</it>infected Taiwanese patients.</p> <p>Results</p> <p>Of the 549 <it>H. pylori-</it>infected patients enrolled, 470 patients (265 with gastritis, 118 with duodenal ulcer, and 87 with gastric ulcer) received SNPs analysis of MMP-3_{-1612 6A > 5A}, MMP-7_{-181 A > G}, MMP-9_{exon 6 A > G}, TIMP-1_{372 T > C}and TIMP-2_{-418 G > C}by PCR-RFLP. The 181 collected <it>H. pylori </it>isolates were detected for the <it>dupA </it>genotype by PCR. The rates of <it>dupA</it>-positive <it>H. pylori </it>infection were similar among patients with duodenal ulcer (22.8%), gastric ulcer (20.0%), and gastritis (25.5%) (<it>p </it>> 0.05). Males had higher rates of duodenal ulcer and gastric ulcer than females (<it>p </it>< 0.01). Of <it>H. pylori</it>-infected patients, the MMP-3 6A6A genotype were more common in patients with duodenal ulcers than in those with gastritis (87.7% <it>vs</it>. 74.9%, <it>p </it>< 0.05) in females. This genotype had a 2.4-fold (95% CI: 1.02-5.66) increased risk of duodenal ulcer, compared to those with the 5A carrier. Combining the MMP-3/TIMP-1 genotype as 6A6A/CC, the risk of duodenal ulcer increased up to 3.6 fold (<it>p </it>< 0.05) in <it>H. pylori-</it>infected females.</p> <p>Conclusions</p> <p>The MMP-3 promoter polymorphism, but not the <it>dupA</it>-status, may correlate with susceptibility to duodenal ulcer after <it>H. pylori </it>infection in Taiwanese females.</p

Identifying Large-Scale RFID Tags Using Non-Cryptographic Approach

In this paper, we propose a new approach to identify a tag of a RFID system in constant time while keeping untraceability to the tag. Our scheme does not use any cryptographic primitives. Instead, we use a line in a plane to represent a tag. The points on the line, which are infinite and different each other, can be used as tag identification. We also explore the scalability of the proposed scheme. The result of experiments showed that a tag of the RFID system over 1,000,000 tags, embedded 3000 gates, can store 559 dynamic identity proofs

An efficient RFID mutual authentication scheme based on ECC

Recently, Radio Frequency Identification (RFID) technique has been widely deployed in many applications, such as medical drugs management in hospitals and missing children searching in amusement parks. The applications basically can be classified into two types: non-public key cryptosystem (PKC)-based and PKC-based. However, many of them have been found to be flawed in the aspect of privacy problem. Therefore, many researchers tried to resolve this problem. They mainly investigated on how low-cost RFID tags can be used in large-scale systems. However, after analyses, we found those studies have some problems, such as suffering physical attack or de-synch attack. Hence, in this paper, we try to design an efficient RFID scheme based on Elliptic Curve Cryptography (ECC) to avoid these problems. After analyses, we conclude that our scheme not only can resist various kinds of attacks but also outperforms the other ECC based RFID schemes in security requirements, with needing only little extra elliptic curve point multiplications

A Novel RFID Authentication Protocol based on Elliptic Curve Cryptosystem

Recently, many researchers have proposed RFID authentication protocols. These protocols are mainly consists of two types: symmetric key based and asymmetric key based. The symmetric key based systems usually have some weaknesses such as suffering brute force, de-synchronization, impersonation, and tracing attacks. In addition, the asymmetric key based systems usually suffer from impersonation, man-in-the-middle, physical, and tracing attacks. To get rid of those weaknesses and reduce the system workload, we adopt elliptic curve cryptosystem (ECC) to construct an asymmetric key based RFID authentication system. Our scheme needs only two passes and can resist various kinds of attacks. It not only outperforms the other RFID schemes having the same security level but also is the most efficient