Interrogating genomic diversity of E. coli O157:H7 using DNA tiling arrays

Here, we describe a novel microarray-based approach for investigating the genomic diversity of Escherichia coli O157:H7 in a semi-high throughput manner using a high density, oligonucleotide-based microarray. This microarray, designed to detect polymorphisms at each of 60,000 base-pair (bp) positions within an E. coli genome, is composed of overlapping 29-mer oligonucleotides specific for 60 equally spaced, 1000-bp loci of the E. coli O157:H7 strain EDL933 chromosome. By use of a novel 12-well microarray that permitted the simultaneous investigation of 12 strains, the genomes of 44 individual isolates of E. coli O157:H7 were interrogated. These analyses revealed more than 150 single nucleotide polymorphisms (SNPs) and several deletions and amplifications in the test strains. Pyrosequencing was used to confirm the usefulness of the novel SNPs by determining their allelic frequency among a collection of diverse isolates of E. coli O157:H7. The tiling DNA microarray system would be useful for the tracking and identification of individual strains of E. coli O157:H7 needed for forensic investigations.     

America’s unreported economy: measuring the size, growth and determinants of income tax evasion in the U.S.

This study empirically investigates the extent of noncompliance with the tax code and examines the determinants of federal income tax evasion in the U.S. Employing a refined version of Feige’s (Staff Papers, International Monetary Fund 33(4):768–881, 1986, 1989) General Currency Ratio (GCR) model to estimate a time series of unreported income as our measure of tax evasion, we find that 18–23% of total reportable income may not properly be reported to the IRS. This gives rise to a 2009 “tax gap” in the range of $390–$390–540 billion. As regards the determinants of tax noncompliance, we find that federal income tax evasion is an increasing function of the average effective federal income tax rate, the unemployment rate, the nominal interest rate, and per capita real GDP, and a decreasing function of the IRS audit rate. Despite important refinements of the traditional currency ratio approach for estimating the aggregate size and growth of unreported economies, we conclude that the sensitivity of the results to different benchmarks, imperfect data sources and alternative specifying assumptions precludes obtaining results of sufficient accuracy and reliability to serve as effective policy guides.