PROJECT SUMMARY Background: Telehealth (or telemedicine), defined as the use of technology to deliver health care, health information, or health education remotely, has become essential to the modern healthcare system. The COVID- 19 pandemic has accelerated the need for the expansion of telehealth services. In response to the pandemic, federal and state governments implemented temporary modifications and policies to support telehealth adoption. However, it is unclear how telehealth policy expansions impact overall health service utilization in the United States health system. In light of the telehealth expansions policy, it is important to evaluate the impact of telehealth on the quality of care, especially in behavioral health care and chronic disease management for patients with cardiometabolic risk (CMR), as telehealth may offer a potential life-course intervention for promoting healthy aging in this area. Specific Aims: The proposed project will (1) evaluate the impact of state-level telehealth payment parity requiring equal reimbursement for in-person and telehealth visits on health service utilization for adults aged 45 to 64 with CMR in commercial insurance (2) assess how telehealth affects health behavior (medication adherence) for middle-aged and older adults aged 45 or above with CMR. (3) assess how telehealth impact on disease-specific quality of care for middle-aged and older adults aged 45 or above with CMR. Approach: The proposed analysis will utilize data from the primary sources: (1) IBM MarketScan Commercial Claims; (2) Medicare fee-for-service Claims. Additional data sources for covariates and instrument variables will come from (1) the CDC COVID-19 tracker; (2) Internet broadband data from FCC and Microsoft. For Aim 1, I will leverage a policy shock of private insurance telehealth payment mandate to identify the causal effects of interest using a difference-in-differences (DiD) estimation framework. For Aim 2 and Aim 3, to overcome potential endogeneity resulting from self-selection and reverse causality in telehealth use and outcomes of interest, I will use a two-stage least squares (2SLS) approach with internet connectivity at the county level as an instrumental variable (IV). I will use the causal inference framework to evaluate the impact of telehealth on medication adherence and disease-specific quality of care for middle-aged and older adults with CMR. Contribution and Significance: This study is significant because limited rigorous evidence indicates how telehealth affects healthcare utilization and quality of care for patients with CMR based on large population studies over an extended period beyond the pandemic. This study will contribute to understanding the impact of telehealth reimbursement policy reform on health service utilization in the U.S. health system. In addition, this study will provide evidence of the causal effects of telehealth on chronic disease management and quality of care for middle-aged and older ...