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Biomedical subjects

Richard F MacLehose

Publications and source records attributed to Richard F MacLehose.

6 recordsLinked to original sources
PubMed2005

Improved estimation of controlled direct effects in the presence of unmeasured confounding of intermediate variables.

Adjusting for a causal intermediate is a common analytic strategy for estimating an average causal direct effect (ACDE). The ACDE is the component of the total exposure effect that is not relayed through the specified intermediate. Even if the total effect is unconfounded, the usual ACDE estimate may be biased when an unmeasured variable affects the intermediate and outcome variables. Using linear programming optimization to compute non-parametric bounds, we develop new ACDE estimators for binary measured variables in this causal structure, and use root mean square confounding bias (RMSB) to compare their performance with the usual stratified estimator in simulated distributions of target populations comprised of the 64 possible potential response types as well as distributions of target populations restricted to subsets of 18 or 12 potential response types defined by monotonicity or no-interactions assumptions of unit-level causal effects. We also consider target population distributions conditioned on fixed outcome risk among the unexposed, or fixed true ACDE in one stratum of the intermediate. Results show that a midpoint estimator constructed from the optimization bounds has consistently lower RMSB than the usual stratified estimator both unconditionally and conditioned on any risk in the unexposed. When conditioning on true ACDE, this midpoint estimator performs more poorly only when conditioned on an extreme true ACDE in one stratum of the intermediate, yet outperforms the stratified estimator in the other stratum when interaction is permitted. An alternate 'limit-modified crude' estimator can never perform less favourably than the stratified estimator, and often has lower RMSB.

Bias↗
PubMed2005

Bounding causal effects under uncontrolled confounding using counterfactuals.

Common sensitivity analysis methods for unmeasured confounders provide a corrected point estimate of causal effect for each specified set of unknown parameter values. This article reviews alternative methods for generating deterministic nonparametric bounds on the magnitude of the causal effect using linear programming methods and potential outcomes models. The bounds are generated using only the observed table. We then demonstrate how these bound widths may be reduced through assumptions regarding the potential outcomes under various exposure regimens. We illustrate this linear programming approach using data from the Cooperative Cardiovascular Project. These bounds on causal effect under uncontrolled confounding complement standard sensitivity analyses by providing a range within which the causal effect must lie given the validity of the assumptions.

Adrenergic beta-Antagonists↗
PubMed2004

Quality of care for acute myocardial infarction in rural and urban US hospitals.

CONTEXT: Acute myocardial infarction (AMI) is a common and important cause of admission to US rural hospitals, as transport of patients with AMI to urban settings can result in unacceptable delays in care. PURPOSE: To examine the quality of care for patients with AMI in rural hospitals with differing degrees of remoteness from urban centers. METHODS: This cohort study used data from the Cooperative Cardiovascular Project (CCP), including 4,085 acute care hospitals (408 remote small rural, 893 small rural, 619 large rural, and 2,165 urban) with 135,759 direct admissions of Medicare beneficiaries ages 65 and older for a confirmed AMI between February 1994 and July 1995. Outcomes included use of aspirin, reperfusion, heparin, and intravenous nitroglycerin during hospitalization; use of beta-blockers, aspirin, and angiotensin-converting enzyme (ACE) inhibitors at discharge; avoidance of calcium channel blockers at discharge; and 30-day mortality. FINDINGS: Substantial proportions of Medicare beneficiaries in both urban and rural hospitals did not receive the recommended treatments for AMI. Medicare patients in rural hospitals were less likely than urban hospitals' patients to receive aspirin, intravenous nitroglycerin, heparin, and either thrombolytics or percutaneous transluminal coronary angioplasty. Only ACE inhibitors at discharge was used more for patients in rural hospitals than urban hospitals. Medicare patients in rural hospitals had higher adjusted 30-day post-AMI death rates from all causes than those in urban hospitals (odds ratio for large rural 1.14 [1.10 to 1.18], small rural 1.24 [1.20 to 1.29], remote small rural 1.32 [1.23 to 1.41]). CONCLUSIONS: Efforts are needed to help hospital medical staffs in both rural and urban areas develop systems to ensure that patients receive recommended treatments for AMI.

Aged↗
PubMed2002

Impact of physician reminders on the use of influenza vaccinations: a randomized trial.

OBJECTIVE: To analyze the impact of mailed physician reminders to immunize their patients. DESIGN: Randomized trial involving Washington State physiatrists participating in the Medicare program. In 1997, all physiatrists in the state were separated into solo or group practice. Solo physicians and group practices were then separately randomized to receive 4 monthly reminders to have their patients immunized. In 1998, the intervention and control groups were switched. SETTING: The state of Washington. PATIENTS: A total of 4300 Medicare outpatients seen in Washington State in 1997 and 4025 patients in 1998. INTERVENTION: Repeated mailer. MAIN OUTCOME MEASURE: By using multivariate analysis, Medicare billing data was analyzed to determine the impact of the physician reminders on influenza vaccination rates. RESULTS: Among solo practitioners, patients whose physiatrist received the reminder letters in 1998 were 34% more likely (adjusted relative risk [RR] = 1.34; 95% confidence interval [CI],.96-1.88) to have a vaccination billing. Among group practitioners, those patients whose physiatrist received the reminder letters in 1997 were 26% more likely (RR = 1.26; 95% CI,.98-1.60) to have a vaccination billing. These differences, however, were not statistically significant. The adjusted RRs for the remaining intervention groups, solo practitioners in 1997 (RR =.89; 95% CI,.63-1.26), and group practitioners in 1998 (RR = 1.00; 95% CI,.73-1.36), revealed no increase in vaccination billings for patients whose physiatrist received the intervention. CONCLUSIONS: Repeated physician reminders did not increase the vaccination rate of Washington State Medicare patients who were seen by physiatrists in 1997 and 1998. These results were consistent whether the physiatrists were in solo or group practice. Other methods should be considered to improve the primary care delivered to this Medicare population.

Aged↗
PubMed2002

Dissatisfaction with medical services among Medicare beneficiaries with disabilities.

OBJECTIVE: To test the hypothesis that Medicare beneficiaries who have difficulties performing activities of daily living (ADLs) are more likely to report dissatisfaction with their health care than those without ADL difficulties. DESIGN: Cross-sectional study. SETTING: Sample from the 1998 Medicare Current Beneficiaries Survey. PARTICIPANTS: A population-based sample (N=19,650) of noninstitutionalized Medicare beneficiaries. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Satisfaction with overall quality and 9 specific aspects of medical services received in the last year. RESULTS: After adjusting for sociodemographic, behavioral, and system characteristics and compared with those without ADL difficulties, Medicare enrollees were more likely to report dissatisfaction with the overall quality of their health care as their number of activity restrictions increased (1-2 ADLs: odds ratio [OR]=1.5; 95% confidence interval [CI], 1.2-2.0; 3-4 ADLs: OR=1.7; 95% CI, 1.2-2.4; 5-6 ADLs: OR=1.9; 95% CI, 1.4-2.8). Analysis of satisfaction with the 9 specific aspects of care yielded similar results. CONCLUSION: Disability is a significant independent risk factor for dissatisfaction with health care in the Medicare population. Efforts should be made to identify individuals with ADL difficulties and to improve their ease and convenience of getting to a doctor, the availability of care off hours, the access to specialists, and the follow-up care received.

Activities of Daily Living↗