title: Instrumental variable methods to assess quality of care the marginal effects of process-of-care on blood pressure change and treatment costs.
abstract: BACKGROUND
  Hypertension is poorly controlled. Team-based care and changes in the process of care have been proposed to address these quality problems. However, assessing care processes is difficult because they are often confounded even in randomized behavioral studies by unmeasured confounders based on discretion of health care providers.
  
  
  OBJECTIVE
  To evaluate the effects of process measures including number of counseling sessions about lifestyle modification and number of antihypertensive medications on blood pressure change and payer-perspective treatment costs.
  
  
  METHODS
  Data were obtained from two prospective, cluster randomized controlled clinical trials (Trial A and B) implementing physician-pharmacist collaborative interventions compared with usual care over six months in community-based medical offices in the Midwest. Multivariate linear regression models with both instrumental variable methods and as-treated methods were utilized. Instruments were indicators for trial and study arms. Models of blood pressure change and costs included both process measures, demographic variables, and clinical variables.
  
  
  RESULTS
  The analysis included 496 subjects. As-treated methods showed no significant associations between process and outcomes. The instruments used in the study were insufficient to simultaneously identify distinct process effects. However, the post-hoc instrumental variable models including one process measure at a time while controlling for the other process demonstrated significant associations between the processes and outcomes with estimates considerably larger than as-treated estimates.
  
  
  CONCLUSIONS
  Instrumental variable methods with combined randomized behavioral studies may be useful to evaluate the effects of different care processes. However, substantial distinct process variation across studies is needed to fully capitalize on this approach. Instrumental variable methods focusing on individual processes provided larger and stronger outcome relationships than those found using as-treated methods which are subject to confounding.
authors.affiliation: Department of Pharmacy Practice and Science, College of Pharmacy, University of Iowa, Iowa City, IA, USA. Electronic address: puttarin@gmail.com.
authors.forename: Puttarin
authors.initials: P
authors.lastname: Kulchaitanaroaj
authors.affiliation: Department of Pharmacy Practice and Science, College of Pharmacy, University of Iowa, Iowa City, IA, USA; Department of Family Medicine, College of Medicine, University of Iowa, Iowa City, IA, USA.
authors.forename: Barry L
authors.initials: BL
authors.lastname: Carter
authors.affiliation: Department of Pharmacy Practice and Science, College of Pharmacy, University of Iowa, Iowa City, IA, USA.
authors.forename: Amber M
authors.initials: AM
authors.lastname: Goedken
authors.affiliation: Department of Epidemiology, College of Public Health, University of Iowa, Iowa City, IA, USA.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Chrischilles
authors.affiliation: Department of Health Services Policy and Management, Arnold School of Public Health, Center for Rehabilitation and Reconstruction Sciences, University of South Carolina, Columbia, SC, USA.
authors.forename: John M
authors.initials: JM
authors.lastname: Brooks
mesh_terms: D000368:Aged; D000959:Antihypertensive Agents / Q000627:therapeutic use; D001794:Blood Pressure / Q000502:physiology; D003299:Cooperative Behavior; D003376:Counseling / Q000379:methods; D003695:Delivery of Health Care / Q000191:economics / Q000458:organization & administration / Q000592:standards; D005260:Female; D017048:Health Care Costs; D006801:Humans; D006973:Hypertension / Q000191:economics / Q000628:therapy*; D008019:Life Style; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D010348:Patient Care Team / Q000191:economics / Q000458:organization & administration / Q000592:standards; D010595:Pharmacists / Q000458:organization & administration*; D010820:Physicians / Q000458:organization & administration*; D011446:Prospective Studies; D011787:Quality of Health Care
chemical_list: D000959:Antihypertensive Agents
keywords: Blood pressure reduction; Costs; Hypertension; Instrumental variable methods; Process of care