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One of the major objectives of this dissertation is to examine the impact of PDPs on healthcare utilizations and costs compared to MA-PDs. This study provided new evidence regarding the impact of PDPs on healthcare use and costs among Medicare beneficiaries. Using nationally representative sample data and an instrumental variable approach to address selection bias, this dissertation found that PDPs had similar annual use and spending for inpatient care. Additionally, PDPs were associated with

significantly higher use and costs for outpatient care and prescription drugs, among community-living Medicare beneficiaries from 2006 to 2010. In the sensitivity analysis,

we found a similar pattern of health resources use and costs, only except the analysis for beneficiaries with LIS. Compared to MA-PDs, PDPs had higher total healthcare costs among beneficiaries with LIS, but had similar healthcare use and costs among

beneficiaries with LIS. Considering the special design of Medicare Part D and LIS, the results from the sensitivity analysis suggest that offering beneficiaries similar drug benefits (e.g., $2/prescription for LIS beneficiaries) may lead to similar healthcare spending. This finding, on the other hand, proves that drug plans with less generous drug plans are associated with higher healthcare spending. Therefore, these results are

consistent with our hypothesis that PDPs have higher costs than MA-PDs after controlling baseline characteristics and favorable selection of MA plans.

Although these two types of Part D plans demonstrate substantial differences on their baseline characteristics that may influence their healthcare use and costs, there was no statistically significant difference in the annual utilizations hospitalizations in both naïve and IV models. In the naïve models, after controlling individual-level

characteristics (e.g., demographics, socioeconomics, health status and functional conditions) and environment characteristics (e.g., number of hospital beds), the results indicate that PDP enrollees had similar annual use of inpatient services, but had 21% higher use of outpatient care, 42% higher use of physician’s office, and 3% higher prescription drugs use, respectively, compared to MA-PD enrollees. Since PDP enrollees are sicker than MA-PD enrollees, they are more likely to have higher use and costs during the study follow-up period. To address the selection bias related to the type of part D plans, we performed IV models and found that PDP enrollees had similar use of

higher likelihood of using outpatient care, and 39% higher likelihood of visiting physician’s office than MA-PD enrollees.

After controlling the baseline characteristics, however, we found that PDPs had higher costs for both prescription drugs and non-drug medication services. PDPs were associated with 15% higher costs of hospitalization, 12% higher costs of outpatient care, 50% higher costs of physician’s office, 26% higher of all types of medical services, and 20% higher of prescription drugs respectively, compared to MA-PD enrollees.

Consequently, PDP enrollees had 25% higher healthcare expenditures than MA-PD enrollees. After controlling the selection bias, the results indicate that PDPs had similar costs for inpatient care, but PDPs were associated with 48% higher costs of outpatient care, 54% higher costs for physician’s office visits, 39% higher of all types of medical services, and 18% higher in prescription drugs respectively, compared to MA-PD enrollees. As a result, PDP enrollees had 30% higher healthcare expenditures than MA- PD enrollees.

Although there are very few studies comparing the healthcare utilizations and expenditures associated with these two types of part D plans, the impact of MA plans compared to FFS has been well-examined in the literature. In the earlier studies, HMOs have shown positive impact on reducing health utilizations and expenditures, compared

to FFS.MA plans were associated with less utilization of overall care, but there was no

clear pattern in the evidence for inpatient care.97 Some data indicated that HMO was associated with a lower rate of preventable hospitalizations and overall hospitalizations, while other studies suggested that HMOs and FFS plans had similar use of inpatient

use, the advantage over FFS was not sustained. By the 2000s, the health services use among HMOs and traditional FFS had converged. This convergence was, in part, attributed to the application of innovated econometric/statistical methods to eliminate selection bias between FFS and MA plans. The favorable selection into HMO has been demonstrated since the introduction of managed care. Captivated payments for HMOs might be the incentives for HMOs to enroll healthy beneficiaries or disenroll those with higher health costs, leading to a healthier and lower-cost population in the HMOs. As a result, we might observe that HMOs had significantly lower costs than FFS plans. In this dissertation, we found that the impact of PDPs was diminished after controlling selection bias, indicating that selection bias may an important role in the differences between PDPs vs MA-PDs. However, the magnitude of the positive outcomes associated with MA-PDs is still unclear. For example, the positive impact of HMOs cannot be fully explained by the selection of healthier beneficiaries into HMOs.97

Another possible explanation for this convergence is that traditional health plans implemented similar cost-saving strategies to HMOs. For example, managed care plans can influence the healthcare utilizations by denying expensive tests or surgical

procedures, restricting access to specialists, and providing payment incentives to providers, which have been recently adopted by FFS. Recent data indicates that FFS plans achieved similar admission rates or length of stay to those of HMOs.194 In addition to direct effects on clinical practices, managed care also has demonstrated influences on the market level.195-197 Improved managed care penetration into the healthcare market is associated with increased competition, leading to changes on the practice patterns in the regional market. There is substantial evidence suggesting that physicians are more likely

to shorten the duration of visits,198and are less likely to provide charity care without any compensation.199,200

In this study, PDPs have generally higher cost-sharing than MA-PDs, and PDP enrollees may face higher drug costs. Based on the economic theory of demand for health services, the demands for health services (including prescription drugs) increase with reduced cost-sharing of drug plans, which has been proven in the RAND study. In the RAND study, the patients with free care (or 0% cost-sharing) used 5 prescriptions monthly, while those with 25% and 50% cost sharing filled 4 prescriptions. Hence, these findings indicated that higher cost-sharing is associated with reduced use of prescription drugs. However, our study found that PDPs had significantly higher annual numbers of prescriptions, which is consistent with published literatures suggesting that HMOs were

associated with lower use of prescription drugs compared to FFS.48 As discussed

previously, PDP enrollees were sicker and had more chronic conditions than MA-PDs, so they may fill more prescriptions and spend more on prescription drugs. Even though we applied the instrumental variable technique to address selection bias, we still found that PDP enrollees had a higher use of prescriptions. This finding may be explained by the price responsiveness that is different for varied conditions. In response to increased cost- sharing, the reduced use of prescriptions was more salient for drugs used to treat

symptoms than those used to treat chronic diseases.158,159 In this study, elderly

beneficiaries had relatively high prevalence of chronic diseases, and may not have been sensitive to the differences in the cost-sharing between these two types of Part D plans, we observed similar utilizations of prescriptions in PDPs and MA-PDs.

HMO’s incentive to use generic drugs. To reduce the drug costs, HMOs influence beneficiaries’ decisions on purchasing generic drugs, by applying higher brand versus generic cost-sharing differentials.201 If patients face high cost differences between brand- name and generic drugs, they are more likely to purchase generic drugs rather than brand- name drugs. This leads to increased use of generic drugs, which are relatively

inexpensive than brand-name drugs.202 In the study, we found MA-PD enrollees were

more likely to use generic drugs than PDP enrollees, which is a possible explanation for the similar costs observed between two groups.

Based on the conceptual framework, environment and individual characteristics are very important factors influencing healthcare use and costs. In this dissertation, we found higher use of healthcare was associated with demographics, socioeconomics, life style (e.g., smoking), regions, health conditions, health altitude, and availability of primary physicians and hospital bed, which are consistent with existing literature. In the sensitivity analysis, two factors, LIS and annual income, were stratified to better

understand the risk factors associated with healthcare use and costs. We found that when Medicare beneficiaries facing similar coinsurance (e.g., $2 copayment for LIS), PDPs had similar impact on healthcare use than MA-PDs, indicating that coinsurance is an important factor determining the use of healthcare. However, PDPs demonstrated similar impact on the use of health services across different levels of annual income, compared to MA-PDs. For example, Weissman et al. reported that increased likelihood of delayed care was observed among patients who are black, low income, uninsured, or without a regular physician.203 Quesenberry et al. indicated that higher BMI is associated with increased use and cost of health services.204