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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 over 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.


  • Undertreatment of primary hyperparathyroidism in a privately insured US population: Decreasing utilization of parathyroidectomy despite expanding surgical guidelines. Surgery Seib, C. D., Meng, T., Suh, I., Cisco, R. M., Lin, D. T., Morris, A. M., Trickey, A. W., Kebebew, E. 2020


    BACKGROUND: Primary hyperparathyroidism is associated with substantial morbidity, including osteoporosis, nephrolithiasis, and chronic kidney disease. Parathyroidectomy can prevent these sequelae but is poorly utilized in many practice settings.METHODS: We performed a retrospective cohort study using the national Optum de-identified Clinformatics Data Mart Database. We identified patients aged ≥35 with a first observed primary hyperparathyroidism diagnosis from 2004 to 2016. Multivariable logistic regression was used to determine patient/provider characteristics associated with parathyroidectomy.RESULTS: Of 26,522 patients with primary hyperparathyroidism, 10,101 (38.1%) underwent parathyroidectomy. Of the 14,896 patients with any operative indication, 5,791 (38.9%) underwent parathyroidectomy. Over time, there was a decreasing trend in the rate of parathyroidectomy overall (2004: 54.4% to 2016: 32.4%, P < .001) and among groups with and without an operative indication. On multivariable analysis, increasing age and comorbidities were strongly, inversely associated with parathyroidectomy (age 75-84, odds ratio 0.50 [95% confidence interval 0.45-0.55]; age ≥85, odds ratio 0.21 [95% confidence interval 0.17-0.26] vs age 35-49; Charlson Comorbidity Index ≥2 vs 0 odds ratio 0.62 [95% confidence interval 0.58-0.66]).CONCLUSION: The majority of US privately insured patients with primary hyperparathyroidism are not treated with parathyroidectomy. Having an operative indication only modestly increases the likelihood of parathyroidectomy. Further research is needed to address barriers to treatment and the gap between guidelines and clinical care in primary hyperparathyroidism.

    View details for DOI 10.1016/j.surg.2020.04.066

    View details for PubMedID 32654861

  • Reply to the Letter to the Editor: How Accurate Are the Surgical Risk Preoperative Assessment System (SURPAS) Universal Calculators in Total Joint Arthroplasty? Clinical orthopaedics and related research Trickey, A. W., Harris, A. H. 2020

    View details for DOI 10.1097/CORR.0000000000001372

    View details for PubMedID 32568891

  • Compounding Benefits of Sentinel Lymph Node Biopsy for Perineal Melanoma: A Population-Based Retrospective Cohort Analysis. Annals of plastic surgery Patel, R. A., Patel, P. D., Ashack, K., Borrelli, M. R., Trickey, A., Wan, D. C. 2020; 84 (5S Suppl 4): S257–S263


    INTRODUCTION: Sentinel lymph node biopsy (SLNB) in the treatment of melanoma is known to provide valuable prognostic information. However, there is no literature describing an overall or disease-specific survival (DDS) benefit of SLNB. In the perineum, melanoma is often more advanced at presentation with current treatment guidelines translated from nonanatomic specific melanoma. As a result, there is little understanding surrounding the role of SLNB in melanoma of the perineum. Our objective is to better understand the therapeutic benefits of SLNB in perineal melanoma.METHODS: The Surveillance, Epidemiology, and End Results program is a large population-based cancer registry including survival data from millions of patients in the United States. The registry was used to generate patient data for analysis from 2004 to 2016. Inclusion criteria included melanoma of the perineum; Breslow depth of 0.80 mm or greater and less than 0.80 mm with ulceration; SLNB or no intervention; clinically negative nodal disease; and available overall survival data.RESULTS: For 879 patients from 2004 to 2016 with perineal melanoma, significant predictors of reduced survival include older than 75 years, Clark level IV-V, Breslow depth of greater than 4.00 mm, positive ulceration status, regional and distant nodal micrometastases, and clinically positive nodes on presentation. Aggregates for overall survival (OS) and disease-specific survival (DSS) were improved with implementation of SLNB. The 5-year survival rates with SLNB versus no SLNB were 54.0% and 43.0% for OS (P = 0.001) and 57.8% and 53.1% for DSS (P = 0.044). Stratification by Breslow depth yielded significant OS and DSS advantage for greater than 1.00 to 2.00 mm (21.3% benefit, P =0.021, and 16.8% benefit, P = 0.044) and greater than 4.00 mm (30.3% benefit, P = 0.005, and 21.0% benefit, P = 0.007) Breslow depths.CONCLUSIONS AND RELEVANCE: Sentinel lymph node biopsy may provide therapeutic benefits in addition to prognostic information for melanoma of the perineum through an increase in 5-year OS.

    View details for DOI 10.1097/SAP.0000000000002388

    View details for PubMedID 32282396

  • Frailty as measured by the Risk Analysis Index is associated with long-term death after carotid endarterectomy. Journal of vascular surgery Rothenberg, K. A., George, E. L., Barreto, N., Chen, R., Samson, K., Johanning, J. M., Trickey, A. W., Arya, S. 2020


    OBJECTIVE: The role of carotid endarterectomy (CEA) continues to be debated in the age of optimal medical therapy, particularly for patients with limited life expectancy. The Risk Analysis Index (RAI) measures frailty, a syndrome of decreased physiologic reserve, which increases vulnerability to adverse outcomes. The RAI better predicts surgical complications, nonhome discharge, and death than age or comorbidities alone. We sought to measure the association of frailty, as measured by the RAI, with postoperative in-hospital stroke, long-term stroke, and long-term survival after CEA. We also sought to determine how postoperative stroke interacts with frailty to alter survival trajectory after CEA.METHODS: We queried the Vascular Quality Initiative CEA procedure and long-term data sets (2003-2017) for elective CEAs with complete RAI case information. For all analyses, the cohort was divided into asymptomatic and symptomatic carotid stenosis. Scoring was defined as not frail (RAI<30), frail (RAI 30-34), and very frail (RAI ≥35). Mortality information through December 2017 was obtained from the Social Security Death Index. Multivariable models (logistic and Cox proportional hazards regressions) were used to study the association of frail and very frail patients with the outcomes of interest. In a post hoc analysis, we created Kaplan-Meier curves to analyze patient mortality after CEA as well as after postoperative stroke.RESULTS: Of the 42,869 included patients, 17,092 (39.9%) were female, and 38,395 (89.6%) were white. There were 25,673 (59.9%) patients assigned to the asymptomatic stenosis group and 17,196 (40.1%) patients in the symptomatic stenosis group. Frailty was not associated with perioperative or long-term postoperative stroke. The risk of long-term mortality was significantly higher for frail (hazard ratio, 1.9 [1.7-2.3]) and very frail (hazard ratio, 3.1 [2.6-3.7]) asymptomatic patients; symptomatic frail and very frail patients also had a two to three times increased risk of long-term mortality. Frail and very frail patients had two to three times the risk for long-term mortality compared with patients who were not frail. Postoperative stroke negatively affected the mortality trajectory for all patients in the cohort, regardless of frailty status.CONCLUSIONS: RAI score is not associated with postoperative stroke; however, frail and very frail status is associated with decreased long-term survival in an incremental fashion based on increasing RAI. RAI assessment should be considered in the preoperative decision-making for patients undergoing CEA to ensure long-term survival and optimal surgical outcomes vs medical management.

    View details for DOI 10.1016/j.jvs.2020.01.043

    View details for PubMedID 32169359

  • Prevalence and Factors Associated With Low-Value Preoperative Testing for Patients Undergoing Carpal Tunnel Release at an Academic Medical Center. Hand (New York, N.Y.) Ding, Q., Trickey, A. W., Mudumbai, S., Kamal, R. N., Sears, E. D., Harris, A. H. 2020: 1558944720906498


    Background: Routine preoperative screening tests before low-risk surgery cannot be justified if the risks to patients are not outweighed by benefits. Several studies and professional guidelines suggest avoiding screening tests prior to minor operations. We aimed to assess the prevalence and patient characteristics associated with low-value preoperative tests (LVTs) prior to carpal tunnel release (CTR) at an academic medical center. Methods: From electronic medical records, we identified patients aged ≥18 who underwent CTR from 2015 to 2017. We determined the occurrence of 9 common LVTs, such as complete blood count (CBC), basic metabolic profile (BMP), and electrocardiogram (ECG), in the 30 days prior to CTR. Multivariable logistic and Poisson regression were used to identify factors associated with receiving any LVT and the number of LVTs, respectively. Results: Among 572 patients, 248 (43.4%) had at least 1 LVT. The most common tests were ECG (31.3% of CTRs), CBC (27.3% of CTRs), and BMP (23.6% of CTRs). Patient factors associated with higher odds of receiving LVT included older age, higher Elixhauser comorbidity score, and general or regional anesthesia (vs monitored anesthesia care). Conclusions: Low-value preoperative tests were frequently received by patients undergoing CTR and were associated with anesthesia type, age, and number of comorbidities. Although our study focused on CTR, these results likely have implications for other commonly performed low-risk procedures. These findings can help guide efforts to improve the quality and value of surgery for carpal tunnel syndrome and facilitate the development of strategies to reduce LVT, such as audit feedback and provider education.

    View details for DOI 10.1177/1558944720906498

    View details for PubMedID 32100568


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