Notes on Causation, Comparison, and Regression

Comparison and contrast are the basic means to unveil causation and learn which treatments work. To build good comparison groups that isolate the average effect of treatment from confounding factors, randomization is key, yet often infeasible. In such non-experimental settings, we illustrate and discuss diagnostics to assess how well the common linear regression approach to causal inference approximates desirable features of randomized experiments, such as covariate balance, study representativeness, interpolated estimation, and unweighted analyses. We also discuss alternative regression modeling, weighting, and matching approaches and argue they should be given strong consideration in empirical work

Observation of the Faraday effect via beam deflection in a longitudinal magnetic field

We report the observation of the magnetic field induced circular differential deflection of light at the interface of a Faraday medium. The difference in the angles of refraction or reflection between the two circular polarization components is a function of the magnetic field strength and the Verdet constant. The reported phenomena permit the observation of the Faraday effect not via polarization rotation in transmission, but via changes in the propagation direction in refraction or in reflection. An unpolarized light beam is predicted to split into its two circular polarization components. The light deflection arises within a few wavelengths at the interface and is therefore independent of pathlength

Balanced and Robust Randomized Treatment Assignments: The Finite Selection Model for the Health Insurance Experiment and Beyond

The Finite Selection Model (FSM) was developed by Carl Morris in the 1970s for the design of the RAND Health Insurance Experiment (HIE) (Morris 1979, Newhouse et al. 1993), one of the largest and most comprehensive social science experiments conducted in the U.S. In the FSM, a treatment group at each of its turns selects the available unit that maximally improves the combined quality of its resulting group of units according to a common optimality criterion. In the HIE and beyond, we revisit, formalize, and extend the FSM as a general tool for experimental design. Leveraging the idea of D-optimality, we propose and analyze a new selection criterion in the FSM. The FSM using the D-optimal selection function has no tuning parameters, is affine invariant, and when appropriate retrieves several classical designs such as randomized block and matched-pair designs. For multi-arm experiments, we propose algorithms to generate a fair and random selection order of treatments. We demonstrate FSM's performance in a case study based on the HIE, a simulation study, and in ten randomized studies from the health and social sciences. We recommend the FSM be considered in experimental design for its conceptual simplicity, efficiency, and robustness

Chiral molecules split light: Reflection and refraction in a chiral liquid

A light beam changes direction as it enters a liquid at an angle from another medium, such as air. Should the liquid contain molecules that lack mirror symmetry, then it has been predicted by Fresnel that the light beam will not only change direction, but will actually split into two separate beams with a small difference in the respective angles of refraction. Here we report the observation of this phenomenon. We also demonstrate that the angle of reflection does not equal the angle of incidence in a chiral medium. Unlike conventional optical rotation, which depends on the path-length through the sample, the reported reflection and refraction phenomena arise within a few wavelengths at the interface and thereby suggest a new approach to polarimetry that can be used in microfluidic volumes

Phylogenetic and functional potential links pH and N2O emissions in pasture soils

This work was funded by the New Zealand Government through the New Zealand Fund for Global Partnerships in Livestock Emissions Research to support the objectives of the Livestock Research Group of the Global Research Alliance on Agricultural Greenhouse Gases (Agreement number: 16084) awarded to SEM and the University of Otago.peer-reviewedDenitrification is mediated by microbial, and physicochemical, processes leading to nitrogen loss via N2O and N2 emissions. Soil pH regulates the reduction of N2O to N2, however, it can also affect microbial community composition and functional potential. Here we simultaneously test the link between pH, community composition, and the N2O emission ratio (N2O/(NO + N2O + N2)) in 13 temperate pasture soils. Physicochemical analysis, gas kinetics, 16S rRNA amplicon sequencing, metagenomic and quantitative PCR (of denitrifier genes: nirS, nirK, nosZI and nosZII) analysis were carried out to characterize each soil. We found strong evidence linking pH to both N2O emission ratio and community changes. Soil pH was negatively associated with N2O emission ratio, while being positively associated with both community diversity and total denitrification gene (nir & nos) abundance. Abundance of nosZII was positively linked to pH, and negatively linked to N2O emissions. Our results confirm that pH imposes a general selective pressure on the entire community and that this results in changes in emission potential. Our data also support the general model that with increased microbial diversity efficiency increases, demonstrated in this study with lowered N2O emission ratio through more efficient conversion of N2O to N2.New Zealand Fund for Global Partnerships in Livestock Emissions Researc

The effects of adding mass to the legs on the energetics and biomechanics of walking.

. Purpose: The metabolic cost of walking increases when mass is added to the legs, but the effects of load magnitude and location on the energetics and biomechanics of walking are unclear. We hypothesized that with leg loading 1) net metabolic rate would be related to the moment of inertia of the leg (I leg ), 2) kinematics would be conserved, except for heavy foot loads, and 3) swing-phase sagittal-plane net muscle moments and swing-phase leg-muscle electromyography (EMG) would increase. Methods: Five adult males walked on a forcemeasuring treadmill at 1.25 mIs j1 with no load and with loads of 2 and 4 kg per foot and shank, 4 and 8 kg per thigh, and 4, 8, and 16 kg on the waist. We recorded metabolic rate and sagittal-plane kinematics and net muscle moments about the hip, knee, and ankle during the single-stance and swing phases, and EMG of key leg muscles. Results: Net metabolic rate during walking increased with load mass and more distal location and was correlated with I leg (r 2 = 0.43). Thigh loading was relatively inexpensive, helping to explain why the metabolic rate during walking is not strongly affected by body mass distribution. Kinematics, single-stance and swing-phase muscle moments, and EMG were similar while walking with no load or with waist, thigh, or shank loads. The increase in net metabolic rate with foot loading was associated with greater EMG of muscles that initiate leg swing and greater swing-phase muscle moments. Conclusions: Distal leg loads increase the metabolic rate required for swinging the leg. The increase in metabolic rate with more proximal loads may be attributable to a combination of supporting (via hip abduction muscles) and propagating the swing leg. Key Words: LOCOMOTION, LEG LOADING, ELECTROMYOGRAPHY, METABOLIC RATE, LOAD CARRIAGE R ecent studies suggest that the primary determinants of the net metabolic rate during walking are performing work to propel the center of mass forward, supporting body weight, and swinging the legs (10-12). Gottschall and Kram (10) estimate that leg swing can account for only about 10% of the net metabolic rate during human walking. Yet, when a modest mass is added to the shank or foot, the metabolic rate during walking increases dramatically (29). A biomechanical explanation for this increase in net metabolic rate during walking has not been clearly established. A better understanding of the relationship between lower-extremity loading and the energetics and biomechanics of walking has practical importance for the study of obesity as well as the design of lower-extremity body armor, prosthetic legs, and powered leg exoskeleton devices. For example, we may gain insight into the effects of increased leg mass, via obesity or body armor, on the net metabolic rate of walking. Also, designers of lowerextremity prosthetic and assistive devices (e.g., powered orthosis) may be able to better estimate how the mass of these devices will affect the energetics and biomechanics of walking. We may also improve our understanding of neuromuscular control strategies that are used during gait. Walking with an external load generally increases metabolic rate. At normal walking speeds, adding a moderate load via a backpack or around the body`s center of mass increases gross metabolic rate in direct proportion to the added mass (i.e., a 20% body weight load results in a 20% increase in metabolic rate) (13). When expressed as net metabolic rate (gross j standing) per kilogram of body mass, the increase is greater than proportional to the load. For example, when walking at 1.5 mIs j1 , Griffin et al. (12) report a 98% increase in net metabolic rate with a load of 50% of body mass. When mass is added to the extremities, metabolic rate increases disproportionately with load and is greater with more distal locations of the load (29). Rose et al. (26) have shown that adding just 2 kg to each foot increased the gross metabolic rate by 30%. Royer and Martin (28) report tha

Hypertension guidelines and coronary artery calcification among South Asians: Results from MASALA and MESA

Untreated hypertension may contribute to increased atherosclerotic cardiovascular disease (ASCVD) risk in South Asians (SA). We assessed HTN prevalence among untreated adults free of baseline ASCVD from the MASALA & MESA studies. The proportion of participants who received discordant recommendations regarding antihypertensive pharmacotherapy use by the 2017-ACC/AHA and JNC7 Guidelines across CAC score categories in each race/ethnic group was calculated. Compared with untreated MESA participants (n = 3896), untreated SA (n = 445) were younger (55±8 versus 59±10 years), had higher DBP (73±10 versus 70±10 mmHg), total cholesterol (199±34 versus 196±34 mg/dL), statin use (16% versus 9%) and CAC=0 prevalence (69% versus 58%), with fewer current smokers (3% versus 15%) and lower 10-year-ASCVD-risk (6.4% versus 9.9%) (all p\u3c0.001). A higher proportion of untreated MASALA and MESA participants were diagnosed with hypertension and recommended anti-hypertensive pharmacotherapy according to the ACC/AHA guideline compared to JNC7 (all p\u3c0.001). Overall, discordant BP treatment recommendations were observed in 9% SA, 11% Whites, 15% Blacks, 10% Hispanics, and 9% Chinese-American. In each race/ethnic group, the proportion of participants receiving discordant recommendation increased across CAC groups (all p\u3c0.05), however was highest among SA (40% of participants). Similar to other race/ethnicities, a higher proportion of SA are recommended anti-hypertensive pharmacotherapy by ACC/AHA as compared with JNC7 guidelines. The increase was higher among those with CAC\u3e100 and thus may be better at informing hypertension management in American South Asians

Ontogenetic Development of Digestive Tract and Enzymes Activity in Hatchery-reared Pink Ear Emperor, Lethrinus lentjan Larvae

Ontogenetic development of the digestive tract and associated organs of Lethrinus lentjan larvae was were learned by observing changes in external morphology, histology, and enzymatic changes from hatchling to 40-day post-hatching (dph). Ontogenetic development of the L. lentjan digestive system can be divided into three major stages; the first stage from hatching of larvae to complete absorption of yolksac, which ends on 2 dph, the second stage from 3 to 15 dph i.e., from exogenous feeding to the formation of the gastric gland and third stage till completion of metamorphosis (35 dph). Pyloric caeca were developed after 20 dph, which was formed entirely by 27 dph. Enzymatic activities of amylase, lipase, trypsin and chymotrypsin were detected before the onset of exogenous feeding and pepsin was detected from 19 dph onwards in L. lentjan. So considering both histology of digestive tract and enzyme development, weaning of L. lentjan larvae to artificial diet can be practiced after 19-20 dph coinciding with the formation of pyloric caeca and production of pepsin enzyme for better digestibility and consequently better growth and survival. The present study can be expended as a reference guide to understand the digestive tract development and successful hatchery rearing of other economically important marine fishe