Betsinger, Sara LinnFor nearly twenty years, federal judges were required to strictly adhere to the federal sentencing guidelines (`the Guidelines"), which calculated sentences based on the offender's current offense level and his or her prior offense history, and which tightly controlled which aggravating and mitigating factors could be considered. However, the U.S. Supreme Court effectively altered the course of federal sentencing with its decision in Booker/Fanfan in 2005, which made the Guidelines advisory; although judges are still required to consider the Guidelines and to provide reasons for departing from their recommendations, Booker has minimized the concern for appellate interference and, as such, has presumably opened the door for increased judicial discretion. The current dissertation examines the impact of the Supreme Court's decision and extends prior work by paying particular attention to its effect on drug and immigration offenses and by incorporating unique dynamic measures to examine contextual changes over time. Because Booker provides a natural experiment, a quasi-experimental pre-test post-test design is employed to examine the decision's impact, with separate models estimated for the full study period (2000-2008), the pre- and post-Booker periods, and each quarter in the study period. In addition, the impact of the decision is examined both through individual-level models, which focus on the role of offense and offender characteristics, and multilevel models, which more closely investigate how Booker's impact may be contextualized by district-level factors. The results provide very little evidence of a "Booker effect" during the years examined; instead, they largely suggest that judges continued to sentence according to pre-Booker sentencing patterns. When noticeable differences were found pre- to post-Booker, closer examination of quarterly trends often revealed that shifts occurred prior to Booker, during the PROTECT Act period. However, because there was initially a large amount of federal-level confusion regarding the interpretation of Booker's application - subsequent clarification was provided by the Supreme Court in Kimbrough and Gall - it is possible that the true effects of Booker became evident well after the study period ended. Future research should expand the types of contextual variables included, incorporate qualitative data, and more precisely estimate Booker's causal influence on sentencing outcomes.enDissertationCriminologyBooker/Fanfandisparitiesjudicial discretionsentencing