scholarly journals Synthetic controls with imperfect pretreatment fit

2021 ◽  
Vol 12 (4) ◽  
pp. 1197-1221 ◽  
Author(s):  
Bruno Ferman ◽  
Cristine Pinto
Keyword(s):  
Synthetic Control ◽  
Difference In Difference ◽  
Specification Test ◽  
Difference Estimator ◽  
Treatment Assignment ◽  
Practical Guidance ◽  
The Difference ◽  
Pre Treatment ◽  
Synthetic Controls ◽  
Theoretical Results

We analyze the properties of the Synthetic Control (SC) and related estimators when the pre‐treatment fit is imperfect. In this framework, we show that these estimators are generally biased if treatment assignment is correlated with unobserved confounders, even when the number of pre‐treatment periods goes to infinity. Still, we show that a demeaned version of the SC method can improve in terms of bias and variance relative to the difference‐in‐difference estimator. We also derive a specification test for the demeaned SC estimator in this setting with imperfect pre‐treatment fit. Given our theoretical results, we provide practical guidance for applied researchers on how to justify the use of such estimators in empirical applications.

scholarly journals Food insecurity patterns before and after initial receipt of Supplemental Security Income

2019 ◽  
Vol 22 (10) ◽  
pp. 1909-1913 ◽  
Author(s):  
Rajan A Sonik ◽  
Susan L Parish ◽  
Monika Mitra
Keyword(s):  
Food Insecurity ◽  
Supplemental Security Income ◽  
Program Participation ◽  
Difference In Difference ◽  
Difference Estimator ◽  
Before And After ◽  
The Usa ◽  
Nationally Representative ◽  
The Difference ◽  
Time Frames

AbstractObjectiveTo assess patterns of food insecurity before and after initial receipt of Supplemental Security Income (SSI) benefits.DesignWe analysed data from a nationally representative sample. We estimated two difference-in-difference models comparing food insecurity patterns among eventual SSI recipients with patterns among eligible non-recipients during two time frames. The first model assessed changes in food insecurity immediately before SSI benefits were first received and the second model assessed changes in food insecurity after programme entry.Setting2008 panel of the Survey of Income and Program Participation.ParticipantsNon-institutionalized population of the USA.ResultsThe percentage of eventual SSI recipients experiencing food insecurity rose from 18 to 30 % in the year before programme entry, compared with a change from 17 to 18 % for eligible non-recipients. Adjusting for sociodemographic covariates, the difference-in-difference estimator for this comparison was statistically significant (P=0·01). Additionally, the percentage of recipients experiencing food insecurity fell from 28 % in the year before programme entry to 16 % in the year after entry, compared with a change from 16 to 17 % for eligible non-recipients. Adjusting for sociodemographic covariates, the difference-in-difference estimator for this comparison was marginally significant (P=0·07).ConclusionsFood insecurity rises prior to SSI entry but may be alleviated by programme benefits. Greater nutritional supports for SSI applicants awaiting decisions may reduce the burden of food insecurity in this population and improve health outcomes.

scholarly journals Influence of the Bottom Color Modification and Material Color Modification Process on the Performance of Modified Poplar

Coatings ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 660
Author(s):  
Qingqing Liu ◽  
Di Gao ◽  
Wei Xu
Keyword(s):  
Chemical Properties ◽  
Target Color ◽  
Modification Process ◽  
Red Color ◽  
The Difference ◽  
Pre Treatment ◽  
Physical And Chemical ◽  
Surface Differentiation ◽  
Color Modification ◽  
And Chemical Properties

According to the old surface coating process of European and American furniture, the surface of modified poplar is first differentiated pre-treatment, and then the bottom color modification and material color modification are respectively applied to the modified poplar after the surface differentiation treatment. The visual physical quantity and physical and chemical properties were measured and compared with mahogany, which is commonly used in old furniture in Europe and America to explore the effect of colorants and coloring steps, as well as different surface pretreatments on the coloring effect. Finally, it is concluded that continuous coloring operations can narrow the difference in brightness and red color value in the coloring layer of modified poplar and mahogany. Continuous coloring operations increase the difference between the yellow-green color values of modified poplar and mahogany. Therefore, the coloring difference between modified poplar and mahogany was affected by the colorant and coloring steps. Through color accumulation, the gap between the two in the target color coloring effect can be reduced, thereby reducing the difference between the coloring effect of modified poplar and mahogany.

scholarly journals Non-submodular model for group profit maximization problem in social networks

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Jianming Zhu ◽  
Smita Ghosh ◽  
Weili Wu ◽  
Chuangen Gao
Keyword(s):  
Social Networks ◽  
Profit Maximization ◽  
Randomized Algorithm ◽  
Political Orientation ◽  
Submodular Functions ◽  
Maximization Problem ◽  
Modular Algorithm ◽  
The Difference ◽  
Group Enterprise ◽  
Theoretical Results

AbstractIn social networks, there exist many kinds of groups in which people may have the same interests, hobbies, or political orientation. Sometimes, group decisions are made by simply majority, which means that most of the users in this group reach an agreement, such as US Presidential Elections. A group is called activated if $$\beta$$ β percent of users are influenced in the group. Enterprise will gain income from all influenced groups. Simultaneously, to propagate influence, enterprise needs pay advertisement diffusion cost. Group profit maximization (GPM) problem aims to pick k seeds to maximize the expected profit that considers the benefit of influenced groups with the diffusion cost. GPM is proved to be NP-hard and the objective function is proved to be neither submodular nor supermodular. An upper bound and a lower bound which are difference of two submodular functions are designed. We propose a submodular–modular algorithm (SMA) to solve the difference of two submodular functions and SMA is shown to converge to a local optimal. We present an randomized algorithm based on weighted group coverage maximization for GPM and apply sandwich framework to get theoretical results. Our experiments verify the efficiency of our methods.

scholarly journals The Use of Heap Bioleaching as a Pre-Treatment for Platinum Group Metal Leaching

2017 ◽  
Vol 262 ◽  
pp. 151-154
Author(s):  
James M. Mwase ◽  
Jochen Petersen
Keyword(s):  
Platinum Group Metal ◽  
Metal Leaching ◽  
Flotation Concentrate ◽  
Group Metal ◽  
Two Samples ◽  
Heap Bioleaching ◽  
Mineral Recovery ◽  
The Difference ◽  
Pre Treatment

Two samples, a Platreef flotation concentrate and coarse ore (<6 mm), were column bioleached at 65°C using a culture dominated by Metallosphaera hakonensis. Based on solution assays, extractions in excess of 90% Cu and Ni were achieved from the flotation concentrate, while from the coarse ore 96% Cu and 67% Ni extractions were achieved. The difference in extraction levels and leaching patterns despite identical conditions used for both samples is discussed, as is the performance of the samples during a follow-up leach step using cyanide to extract the PGMs in a separate column leach experiment. While the recovery of Pd and Au was excellent during these steps, recovery of Pt was limited to 35% after 45 days for the concentrate and 56% after 60 days for the whole ore material, primarily due to the presence of a refractory Pt mineral. Recovery from a concentrate without pre-treatment was substantially lower.

2. Adhesion of the plasma-polymerized fluorocarbon films to silicon substrates The adhesion properties of the plasma-polymerized FC coatings were determined by using a test, already employed by Yasuda and Sharma [13] (see Fig. 1 and Table 1) in which the silicon substrates coated with plasma FC-films were boiled in a0.9% sodium chloride solution. The FC thin films produced in the processes 1 and 2 were lifted after a very short time (15 minutes). Coatings generated in process 3 were lifted after the second cycle of boiling. The films produced in processes 4 and 5 withstood the complete test procedure. The results are shown in Fig. 3. The poor adhesion of the polymerized films in the first two processes is due to the fact that these processes do not involve a plasma pre-treatment process. The difference between processes 1 and 3 is only in the plasma pre-treatment (process 1 does not contain the pre-treatment step of the silicon surface). The fluorocarbon films deposited by processes 4 and 5 have shown the best adhesion. These test results indicate that the plasma pre-treatment is very important and necessary for a good adhesion of the FC coatings to the silicon surfaces. 2.3. Patterning of FC films 2.3.1. Patterning through resist mask. The patterning of the FC films through a photoresist mask (conventional All resist AR-P351) was examined after deposition for process No. 5. Different coating parameters were investigated to improve the adhesion of the resist to the FC surface. The best adhesion results were obtained using the process parameters, shown in Table 3. Differences in the thickness uniformity of so-deposited resists were in a range below 5%. The samples were etched in a pure oxygen plasma in an RIE-system after the lithography steps (pre-bake, exposure, development, post-bake). A resolution of 2 /xm was obtained. A significant increase in the surface energy was not observed after resist stripping. The sessile contact angle of water was 103°. 2.3.2. Lift-off process for patterning thin plasma polymerized FC films. A lift-off process was also examined to pattern the thin FC films. The lithography steps were used before the plasma polymerization process was carried out (Fig. 2). A standard resist AR-P351 was coated directly onto the Si substrates. After all lithography

2014 ◽  
pp. 275-278
Keyword(s):  
Treatment Process ◽  
Test Procedure ◽  
Silicon Surfaces ◽  
Silicon Substrates ◽  
Fluorocarbon Films ◽  
Si Substrates ◽  
Complete Test ◽  
The Difference ◽  
Pre Treatment ◽  
Lift Off

scholarly journals Measuring the sensitivity of difference-in-difference estimates to the parallel trends assumption

2021 ◽  
pp. 263208432110613
Author(s):  
Landon Gibson ◽  
Frederick Zimmerman
Keyword(s):  
Sensitivity Analysis ◽  
Treatment Period ◽  
Treatment Effect ◽  
Statistical Tests ◽  
Sensitivity Analyses ◽  
Difference In Difference ◽  
Control Groups ◽  
Pre Treatment ◽  
Background Difference ◽  
And Control

Background. Difference-in-Difference makes a critical assumption that the changes in the outcomes, over the post-treatment period, are similar between the treated and control groups—the parallel trends assumption. Evaluation of this assumption is often done either by graphical examination or by statistical tests in the pre-treatment period. They result in a binary conclusion about the validity of the assumption. Purpose. This paper proposes a sensitivity analysis that quantifies the departure from parallel trends necessary to meaningfully change the estimated treatment effect. Results. Sensitivity analyses have an advantage over traditional parallel trends tests: they use all available data and thereby work even if only one pre-period is available, and they quantify the strength of unobserved confounder(s) required to change the conclusions of a study. Conclusions. We apply the sensitivity analysis metrics developed by Cinelli and Hazlett (2020) and illustrate them on two studies.

scholarly journals INVESTIGATION ON PRE-TREATMENT PROCESS IN MICROCRYSTALLINE CELLULOSE (MCC) FROM OIL PALM EMPTY FRUIT BUNCH (EFB)

2018 ◽  
Vol 3 (1) ◽  
pp. 87-96
Author(s):  
Muhammad Arif Fahmi Supian ◽  
Khairatun Najwa Mohd Amin ◽  
Saidatul Shima Jamari ◽  
Shahril Mohamad
Keyword(s):  
Microcrystalline Cellulose ◽  
Morphological Characteristics ◽  
Alkaline Treatment ◽  
Empty Fruit Bunch ◽  
Characteristic Peak ◽  
Reinforcing Agent ◽  
Good Potential ◽  
The Mean ◽  
The Difference ◽  
Pre Treatment

In this study, microcrystalline cellulose (MCC) was extracted from empty fruit bunch (EFB) with alkaline treatment, bleaching and acid hydrolysis treatment and its properties were compared with commercial MCC. Two conditions were optimized in this study which are fiber consistency and sodium hydroxide (NaOH) concentration in alkaline pretreatment. The obtained optimum consistency and alkaline concentration are 5% and 20%respectively. The physicochemical and morphological characteristics, elemental composition and size distribution of the obtained alpha cellulose and MCC were analyzed in this work. Fourier transform infrared spectroscopy (FTIR) analysis provided clear evidence that the characteristic peak of lignin and hemicellulose were absent in the spectrum of the alpha cellulose and MCC. The difference in surface morphology and aggregation between alpha cellulose, MCC and commercialized MCC were observed by scanning electron microscopy (SEM). The mean length of approximately 251.3 μm, 41.4 μm and 138.6 μm were measured for alpha cellulose, MCC and commercialized MCC respectively. Thus, the isolated MCC from EFB has a good potential to be utilized as reinforcing agent in green composites and may be a precursor for future roselle derived nanocellulose, and thus a promising subject in nanocomposite research.

Abstract WP46: Blood Pressure, Clinical Improvement And Recanalization Following Acute MCA Occlusion

Stroke ◽  
2013 ◽  
Vol 44 (suppl_1) ◽  
Author(s):  
Nandakumar Nagaraja ◽  
Steven Warach ◽  
Amie W Hsia ◽  
Sungyoung Auh ◽  
Lawrence L Latour ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Clinical Improvement ◽  
Clinical Information ◽  
Collateral Flow ◽  
Stroke Patients ◽  
Mca Occlusion ◽  
The Mean ◽  
The Difference ◽  
Pre Treatment ◽  
B Test

Background: Blood pressure (BP) drop in the first 24 hours after stroke onset may occur in response to vessel recanalization. Clinical improvement could be due to recanalization or better collateral flow with persistent occlusion. We hypothesize that patients with combination of significant improvement on the NIHSS and a drop in BP at 24hr post tPA is associated with recanalization. Methods: We included intravenous t-PA patients from the Lesion Evolution of Stroke Ischemia On Neuroimaging (LESION) registry who had pre-treatment and 24 hour MRA scan, NIHSS scores at those times and an M1 MCA occlusion at baseline, but excluded those on pressors, pre tPA SBP<120 and tandem ICA occlusion. We classified recanalization status on the 24 hour MRA as none, partial or complete. We abstracted all BP measurements for the first 24 hours from the chart and calculated BP drop as the difference of the triage pre-tPA BP and the average of the last 3 hour readings preceding the 24 hour MRI. NIHSS improvement was defined as ≥4points improvement on NIHSS or NIHSS of 0 at 24hour. Patients with combination of drop in BP and NIHSS improvement were compared with others for recanalization status on 24hr MRA by Kendall Tau-b test. Results: Seventeen patients met the study criteria. There were 13 women, the mean age was 76 years and the median baseline NIHSS was 15. On the 24 hour MRA, 3, 8 and 6 patients had none, partial and complete recanalization, respectively. Patients with NIHSS improvement and a SBP drop ≥20 mmHg were more like to have recanalization at 24 hrs (57% Vs 0%, p=0.03). Similar patterns were seen for patients with NIHSS improvement and DBP drop ≥5mmHg (50% Vs 0%, p=0.04) or MAP drop ≥20mmHg (50% Vs 0%, p=0.04). Complete recanalization was only associated with the combination of NIHSS improvement with SBP drop ≥ 20mmHg (66% Vs 0%, p=0.04). A significant association was not found for recanalization with NIHSS improvement alone or drop in BP alone. Conclusion: There is an association of clinical improvement and BP drop in patients who recanalize. Bedside clinical information may be useful in the management of stroke patients.

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