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Help the Biostatistician! What You Need to Know About Estimating Power Calculations and Sample Size


Biostatistician 3, Stanford-Surgery Policy Improvement Research & Education Ctr, Health Services Research Unit


Amber Trickey, PhD, MS, CPH is Senior Biostatistician of the S-SPIRE Center. She supports multidisciplinary teams in research design, implementation, and analysis. In 15 years of health services research, with 8 years focused in surgery, Dr. Trickey has collaborated with diverse investigators, including attending physicians, residents, nurses, psychologists, and engineers. Dr. Trickey obtained degrees in epidemiology and biostatistics, evaluated data quality in trauma care, and led data validation studies using a surgical registry (NSQIP) and administrative claims. Dr. Trickey has contributed to public and private grants on surgical safety, simulation-based training, team communication, error disclosure, and quality metrics.


  • The Comprehensive AO CMF Classification System for Mandibular Fractures: A Multicenter Validation Study. Craniomaxillofacial trauma & reconstruction Mittermiller, P. A., Bidwell, S. S., Thieringer, F. M., Cornelius, C., Trickey, A. W., Kontio, R., Girod, S., and the AO Trauma Classification Study Group, Dana, J., Florian, P., Jia, Q., Johanna, S., Karri, M., Moritz, B., Philipp, G., Stacey, M., Tommy, W., Wenko, S. 2019; 12 (4): 254–65


    The AO CMF has recently launched the first comprehensive classification system for craniomaxillofacial (CMF) fractures. The AO CMF classification system uses a hierarchical framework with three levels of growing complexity (levels 1, 2, and 3). Level 1 of the system identifies the presence of fractures in four anatomic areas (mandible, midface, skull base, and cranial vault). Level 2 variables describe the location of the fractures within those defined areas. Level 3 variables describe details of fracture morphology such as fragmentation, displacement, and dislocation. This multiplanar radiographic image-based AO CMF trauma classification system is constantly evolving and beginning to enter worldwide application. A validation of the system is mandatory prior to a reliable communication and data processing in clinical and research environments. This interobserver reliability and accuracy study is aiming to validate the three current modules of the AO CMF classification system for mandible trauma in adults. To assess the performance of the system at the different precision levels, it focuses on the fracture location within the mandibular regions and condylar process subregions as core components giving only secondary attention to morphologic variables. A total of 15 subjects individually assigned the location and features of mandibular fractures in 200 CT scans using the AO CMF classification system. The results of these ratings were then statistically evaluated for interobserver reliability by Fleiss' kappa and accuracy by percentage agreement with an experienced reference assessor. The scores were used to determine if the variables of levels 2 and 3 were appropriate tools for valid classification. Interobserver reliability and accuracy were compared by hierarchy of variables (level 2 vs. level 3), by anatomical region and subregion, and by assessor experience level using Kruskal-Wallis and Wilcoxon's rank-sum tests. The AO CMF classification system was determined to be reliable and accurate for classifying mandibular fractures for most levels 2 and 3 variables. Level 2 variables had significantly higher interobserver reliability than level 3 variables (median kappa: 0.69 vs. 0.59, p <0.001) as well as higher accuracy (median agreement: 94 vs. 91%, p <0.001). Accuracy was adequate for most variables, but lower reliability was observed for condylar head fractures, fragmentation of condylar neck fractures, displacement types and direction of the condylar process overall, as well as the condylar neck and base fractures. Assessors with more clinical experience demonstrated higher reliability (median kappa high experience 0.66 vs. medium 0.59 vs. low 0.48, p <0.001). Assessors with experience using the classification software also had higher reliability than their less experienced counterparts (median kappa: 0.76 vs. 0.57, p <0.001). At present, the AO CMF classification system for mandibular fractures is suited for both clinical and research settings for level 2 variables. Accuracy and reliability decrease for level 3 variables specifically concerning fractures and displacement of condylar process fractures. This will require further investigation into why these fractures were characterized unreliably, which would guide modifications of the system and future instructions for its usage.

    View details for DOI 10.1055/s-0038-1677459

    View details for PubMedID 31719949

  • Surgery, Stomas, and Anxiety and Depression in Inflammatory Bowel Disease: A Retrospective Cohort Analysis of Privately Insured Patients. Colorectal disease : the official journal of the Association of Coloproctology of Great Britain and Ireland Sceats, L. A., Dehghan, M. S., Rumer, K. K., Trickey, A., Morris, A. M., Kin, C. 2019


    AIM: Inflammatory bowel disease (IBD) patients are diagnosed with anxiety/depression at higher rates than the general population. We aimed to determine the frequency of anxiety/depression among IBD patients and temporal association with abdominal surgery and stoma formation.METHODS: We conducted a retrospective cohort study in adult IBD patients using difference-in-differences methodology using a large commercial claims database (2003-2016). Outcomes were anxiety/depression diagnoses before and after major abdominal surgery or stoma formation.RESULTS: We identified 10,481 IBD patients who underwent major abdominal surgery, 18.8% of whom underwent stoma formation, and 41,924 nonsurgical age- and sex-matched IBD controls who were assigned random index dates. Rates of anxiety and depression increased among all cohorts (p<0.001). Surgical patients had higher odds of anxiety (one surgery: adjusted odds ratio 6.90, 95% confidence interval [6.11-7.79], p<0.001; 2+ surgeries: 7.53 [5.99-9.46], p<0.001) and depression (one surgery: 6.15, [5.57-6.80], p<0.001; 2+ surgeries: 6.88 [5.66-8.36], p<0.001) than nonsurgical controls. Undergoing multiple surgeries was associated with a significant increase in depression from pre- to post-time periods (1.43, [1.18-1.73, p<0.001). Amongst surgical patients, stoma formation was independently associated with anxiety (1.40, [1.17-1.68], p<0.001) and depression (1.23, [1.05-1.45], p=0.01). New ostomates experienced a greater increase in postoperative anxiety (1.24, [1.05-1.47], p=0.01) and depression (1.19, [1.03-1.45], p=0.01) than other surgical patients.CONCLUSIONS: IBD patients who undergo surgery have higher rates of anxiety and depression than nonsurgical patients. Rates of anxiety and depression increase following surgery. Stoma formation represents an additional risk factor. These findings suggest the need for perioperative psychosocial support services.

    View details for DOI 10.1111/codi.14905

    View details for PubMedID 31713994

  • Effect of Acute Stroke Care Regionalization on Intravenous Alteplase Use in Two Urban Counties. Prehospital emergency care : official journal of the National Association of EMS Physicians and the National Association of State EMS Directors Govindarajan, P., Shiboski, S., Grimes, B., Cook, L., Ghilarducci, D., Meng, T., Trickey, A. W. 2019: 1–14


    Importance: Intravenous alteplase is an effective treatment for acute ischemic stroke and is significantly underutilized. It is known that stroke centers with accreditation provide higher intravenous alteplase treatment, and therefore, policies that increase the number of certified stroke centers and the number of acute ischemic stroke patients routed to these centers may be beneficial. Objective: To determine whether increasing access to primary stroke centers (regionalization) led to an increase in intravenous alteplase use in acute ischemic stroke patients. Design: An observational, longitudinal study to examine treatment trends with log-link binomial regression modeling to compare pre-post policy implementation changes in the proportions of patients treated with intravenous alteplase in two counties. Setting: Two urban counties, Santa Clara and San Mateo, in the western region of US that regionalized acute stroke care between 2005 and 2010. Participants: Patients with primary or secondary diagnosis of stroke were identified from the statewide patient discharge database by International Classification of Diseases (ICD-9) codes. We linked ambulance and hospital data to create complete patient care records. Main outcomes and measures: Stroke treatment, defined as a documented primary procedure code for intravenous alteplase administration (ICD-9: 99.10). Results: In Santa Clara County, intravenous alteplase was administered to 35 patients (1.7%) in the pre-regionalization period and 240 patients (2.1%) in the post-regionalization period. In San Mateo County, intravenous alteplase was administered to 29 patients (1.3%) in the pre-policy period and 135 patients (3.2%) in the post-policy period. After regionalization of stroke care, intravenous alteplase increased two-fold in San Mateo County [adjusted RR 2.20, p = 0.003, 95% CI (1.31, 3.69)] but did not show any statistically significant change in Santa Clara County [adjusted RR 1.10, p = 0.55, 95% CI (0.80, 1.51)]. In the post-regionalization phase, when compared with Santa Clara County, we found that San Mateo County had greater change in paramedic stroke detection, higher number of transports to primary stroke centers and more frequent use of intravenous alteplase at stroke centers. Conclusions: Our findings suggest that greater post-regionalization improvements in San Mateo County contributed to significantly better county-level thrombolysis use than Santa Clara County.

    View details for DOI 10.1080/10903127.2019.1679303

    View details for PubMedID 31599705

  • Simplifying Hospital Quality Comparisons for Vascular Surgery Using Center-Level Frailty Burden Rather than Comorbidities George, E. L., Rothenberg, K., Barreto, N. L., Chen, R., Trickey, A. W., Arya, S. ELSEVIER SCIENCE INC. 2019: S163–S164
  • Delayed Fasciotomy Is Associated with Higher Risk of Major Amputation in Patients with Acute Limb Ischemia ANNALS OF VASCULAR SURGERY Rothenberg, K. A., George, E. L., Trickey, A. W., Chandra, V., Stern, J. R. 2019; 59: 195–201


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