Prognostic models and the propensity score.
ABSTRACT Subjects in observational studies of exposure effects have not been randomized to exposure groups and may therefore differ systematically with regard to variables related to exposure and/or outcome. To obtain unbiased estimates and tests of exposure effects one needs to adjust for these variables. A common method is adjustment via a parametric model incorporating all known prognostic variables. Rosenbaum and Rubin propose adjustment by the conditional exposure probability given a set of covariates which they call the propensity score. They show that, at any value of the propensity score, covariates are on average balanced between exposure groups. Thus matching on the propensity score leads to unbiased estimators and tests of exposure effect. However, the validity of the method depends on knowing the exposure probability. This quantity is usually not known in observational studies and needs to be estimated.
- [Show abstract] [Hide abstract]
ABSTRACT: Little is known concerning erroneous surgical procedures of malignant bone tumors, and the prognostic effect of erroneous surgical procedures in osteosarcoma has not been determined. We retrospectively reviewed 240 patients with initially non-metastatic high-grade osteosarcoma of the pelvis and extremities and, of these, identified twenty-six who had undergone previous less appropriate surgical procedures due to misdiagnosis followed by adequate treatment at our institution. We evaluated the clinicopathologic characteristics of these twenty-six patients compared with the remaining 214 patients treated with regular protocol. Subsequently, thirty-eight patients (nineteen in the matched case group and nineteen in the matched control group) were matched for multiple different variables using propensity score matching, and the oncologic results in terms of event-free survival and overall survival were analyzed. The patients undergoing erroneous surgical procedures were typically older, with small, non-osteoblastic-type tumors that were in an unusual location, showed an osteolytic pattern on radiographs, had a tendency toward marginal or intralesional excision with positive histologic margin, and had not been treated with neoadjuvant chemotherapy (all p < 0.05). After adjustment of confounding variables by propensity score matching, there was no significant difference between matched groups with regard to event-free survival (p = 0.46) and overall survival (p = 0.99). Distinct differences existed in the clinicopathologic characteristics of the patients who underwent erroneous surgical procedures due to misdiagnosis. We failed to detect a prognostic relevance of the presence of previous erroneous procedures followed by adequate treatment. Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.The Journal of Bone and Joint Surgery 04/2014; 96(8):e60. · 4.31 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Hip fractures constitute an economic burden on healthcare resources. Most persons with a hip fracture undergo surgery. As morbidity and mortality rates are high, perioperative care leaves room for improvement. Improvement can be achieved if it is organized in comprehensive care pathways, but the effectiveness of these pathways is not yet clear. Hence the objective of this study is to compare the clinical effectiveness of a comprehensive care pathway with care as usual on self-reported limitations in Activities of Daily Living. A controlled trial will be conducted in which the comprehensive care pathway of University Medical Center Groningen will be compared with care as usual in two other, nonacademic, hospitals. In this trial, propensity scores will be used to adjust for differences at baseline between the intervention and control group. Propensity scores can be used in intervention studies where a classical randomized controlled trial is not feasible. Patients aged 60 years and older will be included. The hypothesis is that 15% more patients at University Medical Center Groningen compared with patients in the care-as-usual condition will have recovered at least as well at 6 months follow-up to pre-fracture levels for Activities of Daily Living. This study will yield new knowledge with respect to the clinical effectiveness of a comprehensive care pathway for the treatment of hip fractures. This is relevant because of the growing incidence of hip fractures and the consequent massive burden on the healthcare system. Additionally, this study will contribute to the growing knowledge of the application of propensity scores, a relatively novel statistical technique to simulate a randomized controlled trial in studies where it is not possible or difficult to execute this kind of design.Trial registration: Nederlands Trial Register NTR3171.BMC Musculoskeletal Disorders 10/2013; 14(1):291. · 1.90 Impact Factor