The Costs of Low Birth Weight

Birth weight has emerged as the leading indicator of infant health and welfare and the central focus of infant health policy. This is because low birth weight (LBW) infants experience severe health and developmental difficulties that can impose enormous costs on society. But would the prevention of LBW generate equally sizable cost savings and health improvements? Estimates of the return to LBW-prevention from cross-sectional associations may be biased by omitted variables that cannot be influenced by policy, such as genetic factors. To address this, we compare the hospital costs, health at birth, and infant mortality rates between heavier and lighter infants from all twin pairs born in the United States. We also examine the effect of maternal smoking during pregnancy the leading risk factor for LBW in the United States on health among singleton births after controlling for detailed background characteristics. Both analyses imply substantially smaller effects of LBW than previously thought, suggesting two possibilities: 1) existing estimates overstate the true costs and consequences of LBW by at least a factor of four and by as much as a factor of 20; or 2) different LBW-preventing interventions have different health and cost consequences, implying that policy efforts that presume a single return to reducing LBW will necessarily be suboptimal.

When chiral photons meet chiral fermions - Photoinduced anomalous Hall effects in Weyl semimetals

The Weyl semimetal is characterized by three-dimensional linear band touching points called Weyl nodes. These nodes come in pairs with opposite chiralities. We show that the coupling of circularly polarized photons with these chiral electrons generates a Hall conductivity without any applied magnetic field in the plane orthogonal to the light propagation. This phenomenon comes about because with all three Pauli matrices exhausted to form the three-dimensional linear dispersion, the Weyl nodes cannot be gapped. Rather, the net influence of chiral photons is to shift the positions of the Weyl nodes. Interestingly, the momentum shift is tightly correlated with the chirality of the node to produce a net anomalous Hall signal. Application of our proposal to the recently discovered TaAs family of Weyl semimetals leads to an order-of-magnitude estimate of the photoinduced Hall conductivity which is within the experimentally accessible range.Comment: 9 pages, 4 figure

The Predictive Ability of Statistically-Based Cash-Flow Models: Working Paper Series--09-02

We assess the inter-temporal predictive ability of statistically-based, cash-flow prediction models by extending extant work on annual cash-flow prediction models. Our empirical results consistently underscore the superiority of quarterly cash-flow prediction models estimated on a time-series basis versus cross-sectional models. The superiority of relatively parsimonious, time-series models is consistent with the need to incorporate the firm-specific variability of parameters into expectations rather than restricting such parameters to be constant across firms and time when models are estimated cross-sectionally. Additionally, parsimonious models that employ aggregate earnings data are superior to more complex, disaggregated accrual models. The above results are similar regardless of whether models are estimated using undeflated or deflated variables. These results are particularly salient to researchers and users interested in generating accurate multi-step ahead cash-flow forecasts

The Contextual Nature of the Predicitve Power of Statistically-Based Quarterly Earnings Model: Working Paper Series--05-18

We present new empirical evidence on the contextual nature of the predictive power of five statistically-based quarterly earnings expectation models evaluated on a holdout period spanning the twelve quarters from 2000-2002. In marked contrast to extant time-series work, the random walk with drift (RWD) model provides significantly more accurate pooled, one-step-ahead quarterly earnings predictions for a sample of high-technology firms (n=202). In similar predictive comparisons, the Griffin-Watts (GW) ARIMA model provides significantly more accurate quarterly earnings predictions for a sample of regulated firms (n=218). Finally, the RWD and GW ARIMA models jointly dominate the other expectation models (i.e., seasonal random walk with drift, the Brown-Rozeff (BR) and Foster ARIMA models) for a default sample of firms (n=796). We provide supplementary analyses that document the: 1) increased frequency of the number of loss quarters experienced by our sample firms in the holdout period (2000-2002) vis-a-vis the identification period (1990-1999); 2) reduced levels of earnings persistence for our sample firms relative to earnings persistence factors computed by Baginski et al. (2003) during earlier time periods (1970s - 1980s); 3) relative impact on the predictive ability of the five expectation models conditioned upon the extent of analyst coverage of sample firms (i.e., no coverage, moderate coverage, and extensive coverage); and 4) sensitivity of predictive performance across subsets of regulated firms with the BR ARIMA model providing the most accurate predictions for utilities (n=87) while the RWD model is superior for financial institutions (n=131)

The Time-Series Properties of Quarterly Cash Flows: Working Paper Series--09-12

Considerable advancements in the structural modeling of annual cash flow prediction models have been accomplished in recent years [Dechow et al. (1998) and Barth et al. (2001), among others].Yet, the modeling of quarterly cash flow data has not been as forthcoming due to: (1) the unavailability of sufficiently long time-series data bases of quarterly cash flows reported in accordance with SFAS No. 95 and (2) the presence of seasonality. We provide new empirical findings supportive of the Brown-Rozeff ARIMA model as a candidate statistically-based expectation model for multi-period ahead projections of quarterly cash flows. The Brown-Rozeff ARIMA model provides one-thru-twenty step-ahead projections of quarterly cash flows that are significantly more accurate than those generated by a quarterly time-series, disaggregated-accrual regression model originally popularized by Lorek and Willinger (1996). Although both quarterly earnings and quarterly cash flow from operations are modeled by the same ARIMA structure, we find that the autoregressive and seasonal moving-average parameters of the quarterly earnings model are significantly larger than those of the cash-flow prediction model. This finding is consistent with Beaver (1970) who argues that short-term and long-term accruals induce incremental amounts of serial correlation in the quarterly earnings time series vis-a-vis the time series of quarterly cash flows. These findings are of interest to standard-setting bodies seeking to understand the linkages between accruals and cash flows, analysts who wish to derive multi-step ahead cash flow predictions, and accounting researchers attempting to adopt a statistical proxy for the market's expectation of quarterly cash flows

Time-Series Properties and Predictive Ability of Quarterly Cash Flows: Working Paper Series--06-10

We provide descriptive and predictive evidence on the time-series properties and predictive ability of quarterly cash flows from operations (CFO) reported in accordance with Statement of Financial Accounting Standards (SFAS) No. 95. Previous work such as Hopwood and McKeown (1992) and Lorek, Schaefer and Willinger (1993), among others, has analyzed a proxy series (PCFO) for quarterly cash flows constructed via a relatively simplistic algorithm. We provide new evidence documenting that: (1) the time-series properties of quarterly CFO are at variance with the exclusively seasonal characterization of quarterly PCFO exhibiting both adjacent (quarter-to-quarter) and seasonal (quarter-by-quarter) relationships, (2) the Brown-Rozeff ARIMA model significantly outpredicts the random walk with drift model, seasonal random walk with drift model, and the multivariate time-series regression model (MULT) originally popularized by Lorek and Willinger (1996), (3) the forecast errors of larger firms are significantly smaller than the forecast errors of smaller firms, and (4) the predictive ability of the Brown-Rozeff model is robust. Specifically, we tested it upon an expanded sample of firms (n=745) obtained by eliminating the considerable data requirements of MULT and it exhibited superior predictive power

Analytic Formulation and Numerical Implementation of an Acoustic Pressure Gradient Prediction

The scattering of rotor noise is an area that has received little attention over the years, yet the limited work that has been done has shown that both the directivity and intensity of the acoustic field may be significantly modified by the presence of scattering bodies. One of the inputs needed to compute the scattered acoustic field is the acoustic pressure gradient on a scattering surface. Two new analytical formulations of the acoustic pressure gradient have been developed and implemented in the PSU-WOPWOP rotor noise prediction code. These formulations are presented in this paper. The first formulation is derived by taking the gradient of Farassat's retarded-time Formulation 1A. Although this formulation is relatively simple, it requires numerical time differentiation of the acoustic integrals. In the second formulation, the time differentiation is taken inside the integrals analytically. The acoustic pressure gradient predicted by these new formulations is validated through comparison with the acoustic pressure gradient determined by a purely numerical approach for two model rotors. The agreement between analytic formulations and numerical method is excellent for both stationary and moving observers case