Browsing by Author "Zhang, H"

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    High Prevalence of Cervical Myelopathy among Hip Fracture Patients
    (Operative Techniques in Orthopaedics, 2023-12-01) Zhang, H; Buell, T; Baldwin, E; Dalton, T; Crutcher, C; Abd-El-Barr, MM; Foster, N; Goodwin, CR; Erickson, M
    Hip fractures are devastating injuries for the elderly and an increasing burden to the healthcare system. Cervical spondylotic myelopathy (CSM), as a common cause of disability, instability, and falls in the elderly population, places patients at risk for hip fracture, and myelopathic patients are associated with increased complications after hip surgery. Myelopathy's relationship with hip fractures and impact, however, is not well understood. This study sought to 1) determine the prevalence of CSM among hip fracture patients and 2) hypothesized that hip fractures in CSM patients were associated with greater complexity and costs. In this institutional review board-exempt study, Medicare 1) hip fracture and 2) CSM patients between 2004 and 2014 were identified using the PearlDiver Patient Records Database (PearlDiver Technologies, Inc., CO) with International Classification of Diseases, Ninth Revision, (ICD-9) and Common Procedural Terminology codes. The prevalence of CSM within hip fracture patients was calculated, as was the incidence of hip fractures within CSM patients during this period. Hip fracture patients with CSM were compared with non-CSM hip fracture patients by age, medical comorbidities, average charges/payments, and average lengths of stay (LOS). Hip fracture patients with CSM who underwent cervical surgery were also compared with those who did not undergo cervical surgery, both before and after hip fracture. Statistical analysis with t-test and chi-squared test was performed, with statistical significance set at P < 0.05. Total 22,884 of 2,309,972 hip fracture patients (1.0%) from 2004 to 2014 also had CSM, representing approximately 9900 cases per million persons, higher than previous estimates of the CSM incidence in the general population. These 22,884 hip fracture patients were 4.6% of 496,939 patients with CSM diagnosed during this period, representing a hip fracture incidence of 419 cases per 100,000 persons/year, also higher than previous estimates of hip fracture incidence in the overall population. Hip fracture patients with CSM were significantly younger (P < 0.001) but had significantly greater incidence of hypertension, coronary artery disease, stroke, obesity, tobacco use, diabetes, and osteoporosis (P < 0.001) than non-CSM counterparts, as well as significantly greater average hip fracture-related LOS, per-patient charges, and per-patient payments (P < 0.001). Within this group of hip fractures with CSM, 441 patients (441/22,884; 1.9%) underwent cervical surgery prior to hip fracture, and 245 patients (245/22,884; 1.1%) underwent cervical surgery after hip fracture. These surgically treated patients with CSM were significantly younger but had higher incidence of medical comorbidities (P < 0.001) relative to hip fracture patients with CSM who did not receive cervical surgery at any point. Surgically treated CSM patients also had significantly lower per-patient charges and costs related to their hip fracture care relative to CSM patients with hip fracture who did not receive cervical surgery (P = 0.43, 0.84). This study describes for the first time a high prevalence of CSM in hip fracture patients on a populational level. The 1) prevalence of CSM among hip fracture patients and 2) incidence of hip fractures among CSM patients in this study far exceeded previous epidemiologic estimates. Hip fracture patients with CSM were seen to be significantly younger than hip fracture patients without CSM yet also were seen to have significantly more medical complexity. Hip fracture patients with CSM were also seen to have significantly greater per-patient costs and hip fracture related LOS, findings that are belied by low rates of surgical myelopathy treatment following hip fracture. This study describes for the first time a high prevalence of cervical myelopathy among hip fracture patients on a population level, with implications for both hip fracture prevention and cervical myelopathy diagnosis and treatment.
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    The effect of lead time and demand uncertainties in (r, q) inventory systems
    (Operations Research, 2010-01-01) Song, JS; Zhang, H; Hou, Y; Wang, M
    We study a single-item (r, q) inventory system, where r is the reorder point and q is the order quantity. The demand is a compound-Poisson process. We investigate the behavior of the optimal policy parameters and the long-run average cost of the system in response to stochastically shorter or less-variable lead times. We show that although some of the properties of the base-stock system can be extended to this more general model, some cannot. The same findings also apply when the comparison is conducted on the lead-time demand distributions. © 2010 INFORMS.
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    Volume, volatility, and leverage: A dynamic analysis
    (Journal of Econometrics, 1996-09-01) Tauchen, G; Zhang, H; Liu, M
    This paper uses dynamic impulse response analysis to investigate the interrelationships among stock price volatility, trading volume, and the leverage effect. Dynamic impulse response analysis is a technique for analyzing the multi-step-ahead characteristics of a nonparametric estimate of the one-step conditional density of a strictly stationary process. The technique is the generalization to a nonlinear process of Sims-style impulse response analysis for linear models. In this paper, we refine the technique and apply it to a long panel of daily observations on the price and trading volume of four stocks actively traded on the NYSE: Boeing, Coca-Cola, IBM, and MMM.