904 resultados para Quasi-experimental design


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Over thirty years ago, Leamer (1983) - among many others - expressed doubts about the quality and usefulness of empirical analyses for the economic profession by stating that "hardly anyone takes data analyses seriously. Or perhaps more accurately, hardly anyone takes anyone else's data analyses seriously" (p.37). Improvements in data quality, more robust estimation methods and the evolution of better research designs seem to make that assertion no longer justifiable (see Angrist and Pischke (2010) for a recent response to Leamer's essay). The economic profes- sion and policy makers alike often rely on empirical evidence as a means to investigate policy relevant questions. The approach of using scientifically rigorous and systematic evidence to identify policies and programs that are capable of improving policy-relevant outcomes is known under the increasingly popular notion of evidence-based policy. Evidence-based economic policy often relies on randomized or quasi-natural experiments in order to identify causal effects of policies. These can require relatively strong assumptions or raise concerns of external validity. In the context of this thesis, potential concerns are for example endogeneity of policy reforms with respect to the business cycle in the first chapter, the trade-off between precision and bias in the regression-discontinuity setting in chapter 2 or non-representativeness of the sample due to self-selection in chapter 3. While the identification strategies are very useful to gain insights into the causal effects of specific policy questions, transforming the evidence into concrete policy conclusions can be challenging. Policy develop- ment should therefore rely on the systematic evidence of a whole body of research on a specific policy question rather than on a single analysis. In this sense, this thesis cannot and should not be viewed as a comprehensive analysis of specific policy issues but rather as a first step towards a better understanding of certain aspects of a policy question. The thesis applies new and innovative identification strategies to policy-relevant and topical questions in the fields of labor economics and behavioral environmental economics. Each chapter relies on a different identification strategy. In the first chapter, we employ a difference- in-differences approach to exploit the quasi-experimental change in the entitlement of the max- imum unemployment benefit duration to identify the medium-run effects of reduced benefit durations on post-unemployment outcomes. Shortening benefit duration carries a double- dividend: It generates fiscal benefits without deteriorating the quality of job-matches. On the contrary, shortened benefit durations improve medium-run earnings and employment possibly through containing the negative effects of skill depreciation or stigmatization. While the first chapter provides only indirect evidence on the underlying behavioral channels, in the second chapter I develop a novel approach that allows to learn about the relative impor- tance of the two key margins of job search - reservation wage choice and search effort. In the framework of a standard non-stationary job search model, I show how the exit rate from un- employment can be decomposed in a way that is informative on reservation wage movements over the unemployment spell. The empirical analysis relies on a sharp discontinuity in unem- ployment benefit entitlement, which can be exploited in a regression-discontinuity approach to identify the effects of extended benefit durations on unemployment and survivor functions. I find evidence that calls for an important role of reservation wage choices for job search be- havior. This can have direct implications for the optimal design of unemployment insurance policies. The third chapter - while thematically detached from the other chapters - addresses one of the major policy challenges of the 21st century: climate change and resource consumption. Many governments have recently put energy efficiency on top of their agendas. While pricing instru- ments aimed at regulating the energy demand have often been found to be short-lived and difficult to enforce politically, the focus of energy conservation programs has shifted towards behavioral approaches - such as provision of information or social norm feedback. The third chapter describes a randomized controlled field experiment in which we discuss the effective- ness of different types of feedback on residential electricity consumption. We find that detailed and real-time feedback caused persistent electricity reductions on the order of 3 to 5 % of daily electricity consumption. Also social norm information can generate substantial electricity sav- ings when designed appropriately. The findings suggest that behavioral approaches constitute effective and relatively cheap way of improving residential energy-efficiency.

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Does additional government spending improve the electoral chances of incumbent political parties? This paper provides the first quasi-experimental evidence on this question. Our research design exploits discontinuities in federal funding to local governments in Brazil around several population cutoffs over the period 1982-1985. We find that extra fiscal transfers resulted in a 20% increase in local government spending per capita, and an increase of about 10 percentage points in the re-election probability of local incumbent parties. We also find positive effects of the government spending on education outcomes and earnings, which we interpret as indirect evidence of public service improvements. Together, our results provide evidence that electoral rewards encourage incumbents to spend part of additional revenues on public services valued by voters, a finding in line with agency models of electoral accountability.

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Many authors have discussed a decline in internal labor markets and an apparent shift to a new employment contract, characterized by less commitment between employer and employee and more portable skills. These discussions occur without much evidence on what employment contract employees currently feel is fair. We perfomed quasi-experimental surveys to study when employees in the U.S. andCanada feel that layoffs are fair.Layoffs were perceived as more fair if they were due to lower product demand than if the result of employee suggestions. This result appears to be solely due to norms of reciprocity (companiesshould not punish employees for their efforts), rather than norms of sharing rents, as new technology was also considered a justification for layoffs.Consistent with theories of distributive and procedural equity, layoffs were perceived as more fair if the CEO voluntarily shared the pain. CEO bonuses due to layoffs lowered their reported fairness only slightly.Respondents in Silicon Valley were not more accepting of layoffsthan were those in Canada on average, although the justificationsconsidered valid differed slightly.

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Recent legislations oblige organizations to monitor the effectiveness of internal control mechanisms that are necessary to prevent fraud. However, little is known about the effectiveness of different internal controls. We investigate whether the duty to sign work results-one of the most prominent internal control mechanisms-is effective to prevent fraud under different superior instructions. We use a 2×2 between-subjects experimental design with accountability (duty to sign work results vs. no duty to sign) and superior instructions (with vs. without profit maximization cue) as independent variables. Both manipulations of superior instructions reminded people to respect accounting standards and principles but in one condition, an instruction to increase revenues was integrated as profit maximization cue. We expected this cue to trigger a profit maximization decision frame that increases the likelihood for fraudulent revenue recording. 58 managers from an executive MBA class participated in the experiment. We find that superior instructions interact with accountability. Fraudulent revenue recording was particularly observed when people received instructions to increase revenues and had to sign their work results. Consequently, fraudulent behavior can occur without pressure to commit fraud due to profit maximization cues that are communicated by a superior and despite implemented internal control mechanisms. We discuss possible implications of our results for the prevention of fraudulent behavior.

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Introducció: Teodorico (2004) ens diu que amb el joc cooperatiu els alumnes poden valorar, compartir i reflexionar sobre la relació que estableixen amb els altres companys. Per això, l’objectiu de la meva investigació és avaluar l’efecte que pot tenir l’aplicació d’una unitat de programació, centrada en el joc cooperatiu, en la relació que s’estableix entre els alumnes de 5è de primària, focalitzant l’atenció amb el líder i el menys acceptat del grup-classe. Mètodes: La intervenció s’avalua amb un disseny quasi-experimental pre-post amb grup control. I des del punt de vista dels dissenys observacionals podem parlar d’un disseny de seguiment, idiogràfic i multidimensional. El total de la mostra d’aquesta investigació era de 48 alumnes, dividit en el grup experimental (25) i en el grup control (23). La durada de la intervenció va ser de 8 setmanes i es va utilitzar un qüestionari ad hoc per la confecció dels sociograma i un instrument observacional ad hoc de les relacions de grup-classe. Resultats: El grup experimental estava format per 4 grups d’alumnes, al final de la unitat només se’n formaven 2, en canvi, el grup control, tan abans com després, estava format pels mateixos grups d’alumnes. Un dels menys acceptats del grup experimental ha millorat la relació amb alguns dels companys, en canvi els menys acceptat del grup control no ha millorat cap tipus de relació. Conclusions: Crec que els jocs cooperatius són una bona eina educativa per intentar millorar les relacions, ja que amb més temps crec que els resultats d’aquesta investigació haguessin sigut més positius.

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Objective To evaluate the feasibility of a comprehensive, interdisciplinary adherence program aimed at HIV patients. Setting Two centers of the Swiss HIV Cohort Study: Lausanne and Basel. Method 6-month, pilot, quasi-experimental, 2-arm design (control and intervention). Patients starting a first or second combined antiretroviral therapy line were invited to participate in the study. Patients entering the intervention arm were proposed a multifactorial intervention along with an electronic drug monitor. It consisted of a maximum of six 30-min sessions with the interventionist coinciding with routine HIV check-up. The sessions relied on individualized semi-structured motivational interviews. Patients in the control arm used directly blinded EDM and did not participate in motivational interviews. Main outcome measures Rate of patients' acceptance to take part in the HIV-adherence program and rate of patients' retention in this program assessed in both intervention and control groups. Persistence, execution and adherence. Results The study was feasible in one center but not in the other one. Hence, the control group previously planned in Basel was recruited in Lausanne. Inclusion rate was 84% (n = 21) in the intervention versus 52% (n = 11) in the control group (P = 0.027). Retention rate was 91% in the intervention versus 82% in the control group (P = ns). Regarding adherence, execution was high in both groups (97 vs. 95%). Interestingly, the statistical model showed that adherence decreased more quickly in the control versus the intervention group (interaction group × time P < 0.0001). Conclusion The encountered difficulties rely on the implementation, i.e., on the program and the health care system levels rather than on the patient level. Implementation needs to be evaluated further; to be feasible a new adherence program needs to fit into the daily routine of the centre and has to be supported by all trained healthcare providers. However, this study shows that patients' adherence behavior evolved differently in both groups; it decreased more quickly over time in the control than in the intervention group. RCTs are eventually needed to assess the clinical impact of such an adherence program and to verify whether skilled pharmacists can ensure continuity of care for HIV outpatients.

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Hispanics are a large and growing part of the United States workforce. Projections of the U.S. Census Bureau (2001) state that, by the year 2050, Hispanics will account for 25% of the population. For the Midwest in particular, the Hispanic population is expected to increase 35% by the year 2025. The construction industry is expected to experience a greater percentage increase of its Hispanic population, due to the labor-intensive nature of the industry. This study addresses the expected increase of Hispanic workers in the construction industry by testing the best approaches for delivering training to construction crews with Hispanic workers as well as American supervisors and laborers in the state of Iowa. The research methodology consisted of assessing the effects on communication, safety, work environment, and productivity as a result of the integration training. Results show that integration on-site training decreases workers’ desire to move and increases quality of work and productivity. Most importantly, experimental design was used to show the increasing levels of direct construction communication due to the Toolbox Integration Course for Hispanic Workers and American Supervisors (TICHA) designed as part of this project. This study recommends the creation of a quasi-governmental or association program that can offer continuous research and training that can benefit the construction industry as well as society as a whole. The industry involvement in this process is crucial for contractors. Not only do contractors benefit from reduced insurance premiums when workers act safely, but workers with better communication skills are more productive.

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Self-nanoemulsifying drug delivery systems of gemfibrozil were developed under Quality by Design approach for improvement of dissolution and oral absorption. Preliminary screening was performed to select proper components combination. BoxBehnken experimental design was employed as statistical tool to optimize the formulation variables, X1 (Cremophor® EL), X2 (Capmul® MCM-C8), and X3 (lemon essential oil). Systems were assessed for visual characteristics (emulsification efficacy), turbidity, droplet size, polydispersity index and drug release. Different pH media were also assayed for optimization. Following optimization, the values of formulation components (X1, X2, and X3) were 32.43%, 29.73% and 21.62%, respectively (16.22% of gemfibrozil). Transmission electron microscopy demonstrated spherical droplet morphology. SNEEDS release study was compared to commercial tablets. Optimized SNEDDS formulation of gemfibrozil showed a significant increase in dissolution rate compared to conventional tablets. Both formulations followed Weibull mathematical model release with a significant difference in td parameter in favor of the SNEDDS. Equally amodelistic parameters were calculated being the dissolution efficiency significantly higher for SNEDDS, confirming that the developed SNEDDS formulation was superior to commercial formulation with respect to in vitro dissolution profile. This paper provides an overview of the SNEDDS of the gemfibrozil as a promising alternative to improve oral absorption.

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PURPOSE: Chemokines are implicated in T-cell trafficking. We mapped the chemokine landscape in advanced stage ovarian cancer and characterized the expression of cognate receptors in autologous dendritic cell (DC)-vaccine primed T cells in the context of cell-based immunotherapy. EXPERIMENTAL DESIGN: The expression of all known human chemokines in patients with primary ovarian cancer was analyzed on two independent microarray datasets and validated on tissue microarray. Peripheral blood T cells from five HLA-A2 patients with recurrent ovarian cancer, who previously received autologous tumor DC vaccine, underwent CD3/CD28 costimulation and expansion ex vivo. Tumor-specific T cells were identified by HER2/neu pentamer staining and were evaluated for the expression and functionality of chemokine receptors important for homing to ovarian cancer. RESULTS: The chemokine landscape of ovarian cancer is heterogeneous with high expression of known lymphocyte-recruiting chemokines (CCL2, CCL4, and CCL5) in tumors with intraepithelial T cells, whereas CXCL10, CXCL12, and CXCL16 are expressed quasi-universally, including in tumors lacking tumor-infiltrating T cells. DC-vaccine primed T cells were found to express the cognate receptors for the above chemokines. Ex vivo CD3/CD28 costimulation and expansion of vaccine-primed Tcells upregulated CXCR3 and CXCR4, and enhanced their migration toward universally expressed chemokines in ovarian cancer. CONCLUSIONS: DC-primed tumor-specific T cells are armed with the appropriate receptors to migrate toward universal ovarian cancer chemokines, and these receptors are further upregulated by ex vivo CD3/CD28 costimulation, which render T cells more fit for migrating toward these chemokines. Clin Cancer Res; 21(12); 2840-50. ©2015 AACR.

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This article presents the design and implementation of a progressive resistance strength program adapted to prostate cancer. The initial model corresponds to the guide of the American College Sports Medicine Position Stand (ACSM, 2009). This program includes the most habitual symptoms related to the illness and its treatments. The study design is quasi-experimental. The sample is 33 subjects in treatment phase. Study variables are tumour classification TNM, anthropometric measures, resistance strength, hypertension, fatigue, incontinence, pain and quality of life. After 24 weeks a significant improvement on resistance strength capacity is observed. This result is more consistent in lower extremities. Also improves hypertension, urinary incontinence, pain and quality of life. As conclusion, the improvement of the quality of life is mediated by the functional and physical capacity of the ill person

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The effect of precursors on the anticancer alkaloid production by submerged fermentation using M. anisopliae 3935 was studied, according to complete experimental design 2² with three central points. The results showed that lysine was the most important variable, however, when both lysine and glucose were added to the fermentation medium, the alkaloid production reached, approximately, 17 mg L-1 after 120 hours of fermentation. Then, the scale-up of the process was carried out and these results were confirmed. Finally, 35 mg L-1 of alkaloid at 192 h were attained after increment of added aminoacid lysine.

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This works describes the use of experimental design and surface response methodology for optimization of saponin extraction from Ampelozizyphus amazonicus. For this purpose, a method employing extraction based on maceration assisted by ultrasound technique was utilized. The following factors were studied: extraction length of time and solvent composition. The total saponin was determined by using a gravimetric method and the results expressed by their relative proportion to total crude extract. For the specific condition, 60% hydro-alcoholic solution and 18 minutes extraction length of time has shown the best results. This method can be useful for extraction of substances with biological importance

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In this work, Doehlert experimental design was used to optimize the Transesterification Double Step Process (TDSP) method of methyl soybean oil biodiesel production which starts with a basic catalysis followed by an acidic catalysis. The conversion values were calculated from NMR spectra. Response surface was used to show the results of the interactions between the variables. This experimental design evaluated variables like catalyst and alcohol amount for the basic catalysis and time and temperature for the acidic catalysis. According to results obtained after Doehlert design application the alcohol amount was the main factor that influenced on the basic catalysis but for the acidic catalysis both time and temperature are important and their effects are opposite. It resulted on excellent conversions for both steps obtaining for the basic catalysis about 100% when was used like optimal conditions catalyst amount equal to 0.40 g and volume of methanol equal to 60 mL and for the acidic catalysis about 99% when was used like optimal conditions temperature of 65 °C and 90 minutes for reaction time.

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Maize is a C4 plant that shows few or no response to high [CO2]. Thus, this study aimed to analyze the photosynthetic rate and yield of maize under high [CO2] and develop open-top chambers (OTC) to create an atmosphere enriched with CO2. The experiment was conducted between October 2008 and March 2009. The OTCs were developed in modular scheme. Measurement of photosynthetic rates, transpiration, stomata conductance, grain yield and dry matter were performed. The experimental design was randomized blocks with four replications and three treatments: P1 - plants grown in OTC with 700 ppm [CO2], P2 - plants grown in OTC with environmental [CO2], and P3 - control, cultivated in open field. The results were analyzed by ANOVA and Tukey's test (Pr< 0.05). The chambers can reduce by 25% the photosynthetically active radiation and increase the air and leaf temperatures. Plants under high [CO2] (P1) showed the highest photosynthetic rates and the lowest stomata conductance and transpiration. The total weight of grains (g) and dry mass of shoots (g) showed no increases for P1, despite their higher photosynthetic rates.

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Filtration is a widely used unit operation in chemical engineering. The huge variation in the properties of materials to be ltered makes the study of ltration a challenging task. One of the objectives of this thesis was to show that conventional ltration theories are di cult to use when the system to be modelled contains all of the stages and features that are present in a complete solid/liquid separation process. Furthermore, most of the ltration theories require experimental work to be performed in order to obtain critical parameters required by the theoretical models. Creating a good overall understanding of how the variables a ect the nal product in ltration is somewhat impossible on a purely theoretical basis. The complexity of solid/liquid separation processes require experimental work and when tests are needed, it is advisable to use experimental design techniques so that the goals can be achieved. The statistical design of experiments provides the necessary tools for recognising the e ects of variables. It also helps to perform experimental work more economically. Design of experiments is a prerequisite for creating empirical models that can describe how the measured response is related to the changes in the values of the variable. A software package was developed that provides a ltration practitioner with experimental designs and calculates the parameters for linear regression models, along with the graphical representation of the responses. The developed software consists of two software modules. These modules are LTDoE and LTRead. The LTDoE module is used to create experimental designs for di erent lter types. The lter types considered in the software are automatic vertical pressure lter, double-sided vertical pressure lter, horizontal membrane lter press, vacuum belt lter and ceramic capillary action disc lter. It is also possible to create experimental designs for those cases where the variables are totally user de ned, say for a customized ltration cycle or di erent piece of equipment. The LTRead-module is used to read the experimental data gathered from the experiments, to analyse the data and to create models for each of the measured responses. Introducing the structure of the software more in detail and showing some of the practical applications is the main part of this thesis. This approach to the study of cake ltration processes, as presented in this thesis, has been shown to have good practical value when making ltration tests.