Propensity Score Matching Methods for Non-experimental Causal Studies

This paper considers causal inference and sample selection bias in non-experimental settings in which: (i) few units in the non-experimental comparison group are comparable to the treatment units, and (ii) selecting a subset of comparison units similar to the treatment units is difficult because units must be compared across a high-dimensional set of pre-treatment characteristics. We propose the use of propensity score matching methods and implement them using data from the NSW experiment. Following Lalonde (1986), we pair the experimental treated units with non-experimental comparison units from the CPS and PSID and compare the estimates of the treatment effect obtained using our methods to the benchmark results from the experiment. We show that the methods succeed in focusing attention on the small subset of the comparison units comparable to the treated units and, hence, in alleviating the bias due to systematic differences between the treated and comparison units.

Causal Effects in Non-Experimental Studies: Re-Evaluating the Evaluation of Training Programs

This paper uses propensity score methods to address the question: how well can an observational study estimate the treatment impact of a program? Using data from Lalonde's (1986) influential evaluation of non-experimental methods, we demonstrate that propensity score methods succeed in estimating the treatment impact of the National Supported Work Demonstration. Propensity score methods reduce the task of controlling for differences in pre-intervention variables between the treatment and the non-experimental comparison groups to controlling for differences in the estimated propensity score (the probability of assignment to treatment, conditional on covariates). It is difficult to control for differences in pre-intervention variables when they are numerous and when the treatment and comparison groups are dissimilar, whereas controlling for the estimated propensity score, a single variable on the unit interval, is a straightforward task. We apply several methods, such as stratification on the propensity score and matching on the propensity score, and show that they result in accurate estimates of the treatment impact.

Dissipative Processes in the Early Universe: Bulk Viscosity

In this talk, we discuss one of the dissipative processes which likely take place in the Early Universe. We assume that the matter filling the isotropic and homogeneous background is to be described by a relativistic viscous fluid characterized by an ultra-relativistic equation of state and finite bulk viscosity deduced from recent lattice QCD calculations and heavy-ion collisions experiments. We concentrate our treatment to bulk viscosity as one of the essential dissipative processes in the rapidly expanding Early Universe and deduce the dependence of the scale factor and Hubble parameter on the comoving time $t$. We find that both scale factor and Hubble parameter are finite at $t=0$, revering to absence of singularity. We also find that their evolution apparently differs from the one resulting in when assuming that the background matter is an ideal and non-viscous fluid.Comment: 8 pages, 2 eps figure, Invited talk given at the 7th international conference on "Modern Problems of Nuclear Physics", 22-25 September 2009, Tashkent-Uzbekista

Propensity Score Matching Methods for Non-Experimental Casual Studies

This paper considers casual inference and sample selection bias in non-experimental settings in which: (i) few unites in the non-experimental comparison group are comparable to treatment units; and (ii) selecting a subset of comparison units similar to the treatment units is difficult because units must be compared across a high-dimensional set of pre-treatment characteristics. We propose the use of propensity score matching methods, and implement them using data from the NSW experiment. Following Lalonde (1986), we pair the experimental treated units with non-experimental comparison units from the CPS and PSID, and compare the estimates of the treatment effect obtained using out methods to the benchmark results from the experiment. We show that the methods succeed in focusing attention on the small subset of the comparison units comparable to the treated units and, hence, in alleviating the bias due to systematic differences between the treated and comparison units

Application of chemometry for optimization of liquid chromatographic parameters

Liquid chromatography is one of the most common separation techniques. Optimization of the experimental conditions is a complicated process due to the large number of the variables, which must be simultaneously treated. This mini review summarizes some of the chemometric approaches used in the literature to separate mixtures

Effect of Continuous Education on Readmission Rates for CHF Patients

Aim: To evaluate if continuing the education of Congest Heart Failure patients post-discharge will decrease the amount of readmissions within 6 months of discharge. Background: Causes for decreased readmission rates in Congestive Heart Failure patients have been evaluated in multiple studies. The evaluation of the current research showed having discharge education and post- discharge follow-ups decreased the rate of readmission within 6 months. There is a sufficient amount of evidence supporting the implementation of education upon discharge and follow-ups of Congestive Heart Failure patients. Data Source: Databases and search engines used included: PubMed, OneSearch, CINAHL, DogPile, and Google. Of 25 articles read, 10 articles were included in the review of literature. Results: Three specific forms of patient education were reviewed. These included a telephone follow up program, six months of continued patient education, and a plan tailored to the individual needs of the patient. All three interventions were effective in showing a decrease in readmission rates. Conclusion: Increased time of continued education is believed to be effective in decreasing the readmission of Congestive Heart Failure patients within 30 days of discharge

On the uniqueness of the surface sources of evoked potentials

The uniqueness of a surface density of sources localized inside a spatial region $R$ and producing a given electric potential distribution in its boundary $B_0$ is revisited. The situation in which $R$ is filled with various metallic subregions, each one having a definite constant value for the electric conductivity is considered. It is argued that the knowledge of the potential in all $B_0$ fully determines the surface density of sources over a wide class of surfaces supporting them. The class can be defined as a union of an arbitrary but finite number of open or closed surfaces. The only restriction upon them is that no one of the closed surfaces contains inside it another (nesting) of the closed or open surfaces.Comment: 16 pages, 5 figure

Using some Natural Minerals to Remove Cadmium from Polluted Water

تعد مشكلة ندرة المياه من اهم المشاكل التىتواجه الانسان فى مختلف المجالات المعيشية والاقتصادية مثل مجال الصناعة والزراعة و السياحة مما يدفع الانسان لاستخدام المياه منخفضة الجوده كمياه الصرف الصناعى. ويعتبر استخدام بعض المركبات الكيميائية فى التخلص من العناصر الثقيلة مثل الكادميوم هو نهج ضار بالبيئة. و من المعروف جيدًا أن عنصر الكادميوم يسبب مشاكل كبيرة عند وجوده في الماء ومن ثم يغزو التربة والنباتات والسلسلة الغذائية للإنسان. وبالتالى فان استخدام المواد الطبيعية بدلاً من المواد الكيميائية لإزالة الكادميوم من المياه الملوثة نهجصديقًا للبيئة. لذلك تم التركيز في هذا البحث على استخدام بعض المعادن الطبيعية مثلالمونتموريلونيتوالبنتونيتوالزيوليتلامتصاص عنصر الكادميوم من المياه الملوثة. و قد استخدمت تركيزات مختلفة من الكادميوم في المحاليل 10 و 30 و 50 جزء في المليون و تم معالجتها بثلاث نسب مختلفة لكل معدن (1 و 3 و 5٪ وزن الى حجم). وقد أثبتت النتائج التي تم الحصول عليها أن زيادة نسبة الاضافات إلى 5٪ تزيد من امتزاز الكادميوم من المحلول خاصة عند تركيز 50 جزء في المليون من الكادميوم. حصل الزيوليت على أعلى نسبة امتزاز (47.90 جزء في المليون) ، يليه مونتموريلونيت (44.99 جزء في المليون) وأقل نسبة كانت للبينتونيت (38.97 جزء في المليون). لذلك ، يمكن التوصية بأن إضافة الزيوليت هي المادة الأكثر ملاءمة لإزالة عنصر Cd من المياه الملوثة.Water scarcity is one of the most important problems facing humanity in various fields such as economics, industry, agriculture, and tourism. This may push people to use low-quality water like industrial-wastewater. The application of some chemical compounds to get rid of heavy metals such as cadmium is an environmentally harmful approach. It is well-known that heavy metals as cadmium may induce harmful problems when present in water and invade to soil, plants and food chain of a human being. In this case, man will be forced to use the low quality water in irrigation. Application of natural materials instead of chemicals to remove cadmium from polluted water is an environmental friendly approach. Attention was drawn in this research work to use some natural minerals as zeolite, bentonite and montmorillonite to adsorb cadmium element from polluted water. Various concentrations of cadmium in solutions 10, 30 and 50 ppm were treated with three different ratios of each mineral; 1, 3 and 5% (W/V). The obtained results proved that increasing the ratio of amendments to 5% increased Cd adsorption from solution particularly at 50ppm Cd. Zeolite obtained the highest ratio of adsorption (47.90 ppm), followed by montmorillonite (44.99 ppm) and the lowest was bentonite (38.97 ppm). Therefore, it can be recommended that addition of zeolite is the most favorable material to remove Cd element from polluted water