The Myth of the Reliability Test

The U.S. Supreme Court’s ruling in Daubert v. Merrell Dow Pharmaceuticals, Inc., and subsequent revisions to Federal Rule of Evidence 702, was supposed to usher a reliability revolution. This modern test for admissibility of expert evidence is sometimes described as a reliability test. Critics, however, have pointed out that judges continue to routinely admit unreliable evidence, particularly in criminal cases, including flawed forensic techniques that have contributed to convictions of innocent people later exonerated by DNA testing. This Article examines whether Rule 702 is in fact functioning as a reliability test, focusing on forensic evidence used in criminal cases and detailing the use of that test in states that have adopted the language of the 2000 revisions to Rule 702. Surveying hundreds of state court cases, we find that courts have largely neglected the critical language concerning reliability in the Rule. Rule 702 states that an expert may testify if that testimony is “the product of reliable principles and methods,” which are “reliably applied” to the facts of a case. Or as the Advisory Committee puts it simply, judges are charged to “exclude unreliable expert testimony.” Judges have not done so in state or federal courts, and in this study, we detail how that has occurred, focusing on criminal cases

Using x ray images to detect substructure in a sample of 40 Abell clusters

Using a method for constraining the dynamical state of a galaxy cluster by examining the moments of its x-ray surface brightness distribution, we determine the statistics of cluster substructure for a sample of 40 Abell clusters. Using x-ray observations from the Einstein Observatory Imaging Proportional Counter (IPC), we measure the first moment M1(r), the ellipsoidal orientation angle theta2(r), and the axial ratio eta(r) at several different radii in the cluster. We determine the effects of systematics such as x-ray point source emission, telescope vignetting, Poisson noise, and characteristics of the IPC by measuring the same parameters on an ensemble of simulated cluster images. Due to the small band-pass of the IPC, the ICM emissivity is nearly independent of temperature so the intensity at each point in the IPC images is simply proportional to the emission measure calculated along the line of sight through the cluster (e.g. Fabricant et al. 1980). Therefore, barring a change superposition of two x-ray emitting clusters, a significant variation in the image centroid M1(r) as a function of radius indicates that the center of mass of the intra-cluster medium (ICM) varies with radius. We argue that such a configuration (essentially an m = 1 component in the ICM density distribution) is a non-equilibrium component; it results from an off-center subclump or a recent merger in the ICM

Genetic Map of Bacteriophage [var phi]X174

Bacteriophage [var phi]X174 temperature-sensitive and nonsense mutations in eight cistrons were mapped by using two-, three-, and four-factor genetic crosses. The genetic map is circular with a total length of 24 × 10−4wt recombinants per progeny phage. The cistron order is D-E-F-G-H-A-B-C. High negative interference is seen, consistent with a small closed circular deoxyribonucleic acid molecule as a genome

μ\mu--PhotoZ: Photometric Redshifts by Inverting the Tolman Surface Brightness Test

Surface brightness is a fundamental observational parameter of galaxies. We show, for the first time in detail, how it can be used to obtain photometric redshifts for galaxies, the $\mu$-PhotoZ method. We demonstrate that the Tolman surface brightness relation, $\mu \propto (1+z)^{-4}$, is a powerful tool for determining galaxy redshifts from photometric data. We develop a model using $\mu$ and a color percentile (ranking) measure to demonstrate the $\mu$-PhotoZ method. We apply our method to a set of galaxies from the SHELS survey, and demonstrate that the photometric redshift accuracy achieved using the surface brightness method alone is comparable with the best color-based methods. We show that the $\mu$-PhotoZ method is very effective in determining the redshift for red galaxies using only two photometric bands. We discuss the properties of the small, skewed, non-gaussian component of the error distribution. We calibrate $\mu_r, (r-i)$ from the SDSS to redshift, and tabulate the result, providing a simple, but accurate look up table to estimate the redshift of distant red galaxies.Comment: Accepted for publication in the Astronomical Journa

Cosmological constraints from cluster x-ray morphologies

We use a representative sample of 65 galaxy clusters observed with the Einstein IPC to constrain the range of cluster X-ray morphologies. We develop and apply quantitative and reproducible measures to constrain the intrinsic distributions of emission weighted centroid variation, axial ratio, orientation, and the radial fall--off. We then use the range of cluster X--ray morphologies to constrain three generic cosmological models (Omega=1, Omega_0=0.2, and Omega_0=0.2 & lambda_0=0.8). For each of these models, we evolve eight sets of Gaussian random initial conditions consistent with an effective power spectrum P(k)\propto k^{-1} on cluster scales. Using this sample of 24 numerical cluster simulations, we compare the X--ray morphologies of the observed and simulated clusters. The comparisons indicate that: (i) cluster centroid variations, axial ratios, and radial fall-offs are sensitive to the underlying cosmological model, and (ii) galaxy clusters with the observed range of X--ray morphologies are very unlikely in low Omega_0 cosmologies. The analysis favors the Omega=1 model, though some discrepancies remain. We discuss the effects of changing the initial conditions and including additional physics in the simulations