This dissertation is related to the areas of labor, education, and health economics. In a dramatic reversal from the recent past decades, more women than men now attend college in the U.S. and worldwide. Meanwhile, both male and female marriage rates have declined, especially for younger cohorts. Chapters 1 and 2 focus on the implications of the changing gender dynamics in colleges in the U.S. by examining the short- and long-term impacts of college sex ratios. College campus provides a unique setting of a bustling dating market with a more considerable variation of sex ratios than existing literature. The impacts of sex ratios can be explained by Becker's marriage market model via two channels. The channel of available mates suggests that the scarcer gender would expose to more opportunities for partnership. The channel of bargaining power indicates that the scarcer gender would obtain a larger bargaining power that shifts the dating/marriage market in their favor. Chapter 1 looks at how the male-to-female sex ratios in four-year higher education institutions of the U.S. impact students' outcomes in marriage, own earnings, and spouse's earnings by utilizing nearly universal data on statistics of students' performances at the college level. A rich set of college-level variables are controlled to address the potential bias that certain types of students may sort into colleges with characteristics correlated with the sex ratio. It finds that the increase of sex ratios has significant positive effects on women's marriage rates and their spouse's earnings, but a trivial negative impact on their earnings. Higher sex ratios also appear to have increased men's future earnings after graduation. The magnitude of the effect decays with a further increase of sex ratios, which can be theoretically verified by Becker's model. Besides, the impact of sex ratios on marriage rates appears to be stronger in religious-affiliated colleges where the student culture can be more conservative and in young campuses where the vast majority of students are aged 25 or below. As the hookup culture prevalent in American colleges in recent years, Chapter 2 examines how the imbalanced college male-to-female ratios impact students' dating-related behaviors and attitudes by utilizing rich individual-level data. The richness of the data allows me to include a series of control variables -- i.e., demographic characteristics, majors, the choice of residence, the status of fraternity or sorority, sexual histories, and attitudes of liberal tendency -- to address the potential omitted variable bias. It also allows me to construct three groups of dating-related behaviors and attitudes indices as outcomes. Consistent with the theoretical prediction, I find those female students have a more significant probability of participating in a dating scene at the same campus with the increase of available male mates. Also, both men and women decrease their participation in casual sexual activities when the male-to-female ratio increases on campus. The effect of sex ratios is found for men in Greek organizations. With the increase of potential competitors in the dating market, men are less likely to participate in a dating scene and feel less empowered. Over the past three decades, a number of states in the U.S. have liberalized scope-of-practice laws allowing nurse practitioners to practice in some domains without a physician's involvement independently. Chapter 3 is a joint study with Dr. Mindy Marks and Dr. Angela Kilby to analyze the impact of these laws on access to medication-assisted substance use disorder treatment. Using two natural experiments and rich address-level practitioner data, we show that liberalizations of nurse practitioner prescribing authority led to a sizable improvement in access to medication-assisted treatment, especially in underserved, rural areas. Counterintuitively, we find that expanding non-physician practice authority increases access to care provided by physicians and shows that this is entirely driven by complementarities between physicians and nurse practitioners with full prescriptive authority who practice together to provide substance use disorder care. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]