Discrete-time survival analysis as an educational research technique has focused on analysing and interpretating parameter estimates. The purpose of this study was to examine the effects of certain data characteristics on the hazard estimates and goodness of fit statistics. Fifty-four simulated data sets were crossed with four conditions in a 2 (time period) by 3 (distribution of Y = 1) by 3 (distribution of Y = 0) by 3 (sample size) design.

Thesis advisor: Henry I. Braun / The City Connects intervention is motivated by the belief that out-of-school factors act as barriers to student thriving in cognitive and non-cognitive domains. It seeks to address these barriers first by identifying each student’s strengths and needs and then by providing a tailored set of prevention, intervention, and enrichment programs. Underlying the program is the assumption that provision of high-quality resources and individualized services will enable children to be cognitively, socio-emotionally, and physically prepared to thrive in school. This study’s purpose was to estimate the effects of the City Connects intervention on English learners’ (EL) likelihood of exiting Limited English Proficiency (LEP) status. ELs comprise a student subpopulation most at-risk to fail academically, and exposure to the program was hypothesized to improve their likelihood of exiting LEP status earlier than otherwise. A series of one- and two-level discrete-time event history analyses were conducted on the main analytic sample as well as two sub-samples. As participation in City Connects is at the school-level, school-level matching was used for sub-samples 1 and 2, and propensity score weights were applied at the student-level for all three samples. Additionally, hazard probabilities, survival probabilities, cumulative hazard rates, and median lifetimes were estimated. Lastly, a sensitivity analysis was conducted to examine whether effects were robust to unobserved selection bias. The results indicated that ELs participating in the City Connects intervention were significantly more likely to exit LEP status earlier than their peers in comparison schools. The median time in LEP status in City Connects schools was shorter and translated into a gain of at least one half of a year in grade in mainstream classes. Also, all the fitted models indicated that approximately 10 percent more City Connects students exited LEP status by the end of fifth grade than comparison students. Findings highlight the impact of the City Connects intervention, as ELs entering mainstream classes earlier could translate into important academic and non-academic gains, such as improved academic achievement and increased self-confidence. / Thesis (PhD) — Boston College, 2017. / Submitted to: Boston College. Lynch School of Education. / Discipline: Educational Research, Measurement and Evaluation.

The purpose of this dissertation is threefold: to determine the differences in apparent prevalence and the antimicrobial susceptibility of Campylobacter spp. between antimicrobial-free and conventional swine farms; secondly, to introduce an appropriate statistical model to compare the minimum inhibitory concentration distributions of Escherichia coli and Campylobacter spp. isolated from both farm types; and thirdly, to examine the potential herd level risk factors that may be associated with antimicrobial resistance of Campylobacter spp. and E. coli isolates from finishers on antimicrobial-free and conventional farming systems. In addition, a critical review of studies that have compared the levels and patterns of antimicrobial resistance among animals from antimicrobial-free and conventional farming practices was performed. Fecal samples from 15 pigs were collected from each of 35 antimicrobial-free and 60 conventional farms in the Midwestern U.S. Campylobacter spp. was isolated from 464 of 1,422 fecal samples, and each isolate was tested for susceptibility to 6 antimicrobials. The apparent prevalence of Campylobacter spp. isolates was approximately 33 percent on both conventional and antimicrobial-free farms. The proportion of antimicrobial resistance among Campylobacter was higher for three antimicrobials within conventional compared to antimicrobial-free farms. The susceptibilities of populations of bacteria to antimicrobial drugs were summarized as minimum inhibitory concentration (MIC) frequency distributions. The use of MIC values removed the subjectivity associated with the choice of breakpoints which define an isolate as susceptible or resistant. A discrete-time survival analysis model was introduced as the recommended statistical model when MICs are the outcome. A questionnaire was completed by each farm manager on biosecurity, preventive medication, vaccines, disease history, and production management. Multivariable population-averaged statistical models were used to determine the relationships among antimicrobial susceptibility patterns and potential herd-level risk factors. Controlling for herd type (antimicrobial-free versus conventional), each antimicrobial-bacterial species combination yielded unique combinations of risk factors; however, housing type, history of rhinitis, farm ventilation, and history of swine flu were significant in more than one model. A variety of herd-level practices were associated with the prevalence of antimicrobial resistance on swine farms. Further studies are encouraged when considering interventions for antimicrobial resistance on both antimicrobial-free and conventional farms.