Testing equality of variances in the analysis of repeated measurements

The problem of comparing the precisions of two instruments using repeated measurements can be cast as an extension of the Pitman-Morgan problem of testing equality of variances of a bivariate normal distribution. Hawkins (1981) decomposes the hypothesis of equal variances in this model into two subhypotheses for which simple tests exist. For the overall hypothesis he proposes to combine the tests of the subhypotheses using Fisher's method and empirically compares the component tests and their combination with the likelihood ratio test. In this paper an attempt is made to resolve some discrepancies and puzzling conclusions in Hawkins's study and to propose simple modifications.\ud \ud The new tests are compared to the tests discussed by Hawkins and to each other both in terms of the finite sample power (estimated by Monte Carlo simulation) and theoretically in terms of asymptotic relative efficiencies

Conicoid Mirrors

The first order equation relating object and image location for a mirror of arbitrary conic-sectional shape is derived. It is also shown that the parabolic reflecting surface is the only one free of aberration and only in the limiting case of distant sources.Comment: 9 page

With a little help from my friends: Developing an assisted automated peritoneal dialysis program in Western Australia

Background: Nurse-assisted automated peritoneal dialysis (AAPD) offers a model of care that has been successfully used in frail dialysis populations internationally. AAPD offers cost savings over hospitalisation on peritoneal dialysis (PD) or in-centre haemodialysis (HD). Method: A pilot AAPD model of care was developed in Western Australia (WA). Patient evaluation was measured utilising a perceptions of dialysis survey, clinical events, hospitalisation and peritonitis rates, Charlson Comorbidity Index (CCI), KDQoL-SF 36 and a survey. Staff opinions and perceived competency were measured by an online survey. Economic analysis was undertaken. Results: A successful collaborative model was developed. 40 staff were trained and competency significantly improved during program delivery (p < 0.0001). 15 patients with an average CCI score of 8.7 used the service for 18 periods of care over 18 months (mean 33 days SD 47). Two non-renal cause deaths and two episodes of peritonitis occurred. Patient opinions were extremely positive. Cost savings were estimated at $620,000. Conclusion: In WA, an AAPD pilot program has been successfully developed and delivered. A sustainable model has overcome initial hurdles. Staff have gained new skills and delivered effective care, demonstrated by high patient acceptance. The program was cost-effective compared to staying in hospital or transferring to HD

System for the measurement of ultra-low stray light levels

An apparatus is described for measuring the effectiveness of stray light suppression light shields and baffle arrangements used in optical space experiments and large space telescopes. The light shield and baffle arrangement and a telescope model are contained in a vacuum chamber. A source of short, high-powered light energy illuminates portions of the light shield and baffle arrangement and reflects a portion of same to a photomultiplier tube by virtue of multipath scattering. The resulting signal is transferred to time-channel electronics timed by the firing of the high energy light source allowing time discrimination of the signal thereby enabling the light scattered and suppressed by the model to be distinguished from the walls and holders around the apparatus

The Versatility of Scanning Electron Microscopy in Thin Film Device Analysis

The versatility of scanning electron microscopy is shown for many stages of fabrication of thin film transistor driver matrices for actively addressed liquid crystal displays. Electron channeling and Schottky barrier charge collection modes allow rapid assessment of silicon crystal quality. The secondary electron mode allows examination of conductor lead crossover integrity. A form of voltage contrast is used on the completed array to monitor performance of the array prior to liquid crystal filling

A Fast Algorithm for Robust Regression with Penalised Trimmed Squares

The presence of groups containing high leverage outliers makes linear regression a difficult problem due to the masking effect. The available high breakdown estimators based on Least Trimmed Squares often do not succeed in detecting masked high leverage outliers in finite samples. An alternative to the LTS estimator, called Penalised Trimmed Squares (PTS) estimator, was introduced by the authors in \cite{ZiouAv:05,ZiAvPi:07} and it appears to be less sensitive to the masking problem. This estimator is defined by a Quadratic Mixed Integer Programming (QMIP) problem, where in the objective function a penalty cost for each observation is included which serves as an upper bound on the residual error for any feasible regression line. Since the PTS does not require presetting the number of outliers to delete from the data set, it has better efficiency with respect to other estimators. However, due to the high computational complexity of the resulting QMIP problem, exact solutions for moderately large regression problems is infeasible. In this paper we further establish the theoretical properties of the PTS estimator, such as high breakdown and efficiency, and propose an approximate algorithm called Fast-PTS to compute the PTS estimator for large data sets efficiently. Extensive computational experiments on sets of benchmark instances with varying degrees of outlier contamination, indicate that the proposed algorithm performs well in identifying groups of high leverage outliers in reasonable computational time.Comment: 27 page