Introducing a statistical model of noise in terms of the covariance matrix of the N-vector, we point out that the least-squares conic fitting is statistically biased. We present a new fitting scheme called renormalization for computing an unbiased estimate by automatically adjusting to noise. Relationships to existing methods are discussed, and our method is tested using real and synthetic data.

the hotelling's  control chart, is the most widely used multivariate procedure for monitoring  two or more related quality characteristics, but it’s power lacks the desired performance in detecting small to moderate shifts. recently, the variable sampling intervals (vsi) control scheme in which the length of successive sampling intervals is determined upon the preceding values has been pro...

INTRODUCTION HIV testing is a cornerstone of efforts to combat the HIV epidemic, and testing conducted as part of surveillance provides invaluable data on the spread of infection and the effectiveness of campaigns to reduce the transmission of HIV. However, participation in HIV testing can be low, and if respondents systematically select not to be tested because they know or suspect they are HI...

Hellerstein and Neumark (1999) developed a very straightforward method to detect wage discrimination using matched employer-employee data. However it may produce biased estimates whenever there is not perfect competition in the labor market or when the discriminated group is segregated into good or bad firms. The purpose of this paper is to develop a test for wage discrimination that completes ...

Two meta-analyses review the effectiveness of incentives in Web studies. The first analysis summarizes 32 experiments on the impact of material incentives on response. It is based on a sample of 212,810 people. A significant effect (odds ratio = 1.19; 95% confidence interval: 1.13—1.25) is revealed, indicating that incentives motivate people to start a Web survey. The second analysis comprises ...

The impact of selection bias on the results of clinical trials has been analyzed extensively for trials of two treatments, yet its impact in multi-arm trials is still unknown. In this paper, we investigate selection bias in multi-arm trials by its impact on the type I error probability. We propose two models for selection bias, so-called biasing policies, that both extend the classic guessing s...

We present a series of statistical tests using homogeneous data and measurements for a sample of Seyfert galaxies. These galaxies were selected from mostly isotropic properties, their far infrared fluxes and warm infrared colors, which provide a considerable advantage over the criteria used by most investigators in the past, like ultraviolet excess. Our results provide strong support for a Unif...

In this article, we propose a new probabilistic model for the distribution of ranks of elliptic curves in families of fixed Selmer rank, and compare the predictions with previous results, and with the databases of curves over the rationals that we have at our disposal. In addition, we document a phenomenon we refer to as Selmer bias that seems to play an important role in the data and in our mo...

OBJECTIVE Missing data are a pervasive problem, often leading to bias in complete records analysis (CRA). Multiple imputation (MI) via chained equations is one solution, but its use in the presence of interactions is not straightforward. STUDY DESIGN AND SETTING We simulated data with outcome Y dependent on binary explanatory variables X and Z and their interaction XZ. Six scenarios were simu...