Heterogeneous Heterogeneity by Default: Testing Categorical Moderators in Random-effects Meta-Analysis

Categorical moderators are often included in mixed-effects meta-analysis to explain heterogeneity in effect sizes. An assumption in tests of moderator effects is that of a constant between-study variance across all levels of the moderator. Although it rarely receives serious thought, there can be drastic ramifications to upholding this assumption. We propose that researchers should instead assume unequal between-study variances by default. To achieve this, we suggest using a mixed-effects location-scale model (MELSM) to allow group-specific estimates for the between-study variances. In two extensive simulation studies, we show that in terms of Type I error and statistical power, nearly nothing is lost by using the MELSM for moderator tests, but there can be serious costs when a mixed-effects model with equal variances is used. Most notably, in scenarios with balanced sample sizes or equal between-study variance, the Type I error and power rates are nearly identical between the mixed-effects model and the MELSM. On the other hand, with imbalanced sample sizes and unequal variances, the Type I error rate under the mixed-effects model can be grossly inflated or overly conservative, whereas the MELSM excellently controlled the Type I error across all scenarios. With respect to power, the MELSM had comparable or higher power than the mixed-effects model in all conditions where the latter produced valid (i.e., not inflated) Type 1 error rates. Altogether, our results strongly support that assuming unequal between-study variances is preferred as a default strategy when testing categorical moderators

484. Identification of Early Features to Differentiate Hospitalized Children Admitted for Suspected MIS-C from Alternative Diagnoses

Background Multi-system inflammatory syndrome in children (MIS-C) is a rare consequence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). MIS-C shares features with common infectious and inflammatory syndromes and differentiation early in the course is difficult. Identification of early features specific to MIS-C may lead to faster diagnosis and treatment. We aimed to determine clinical, laboratory, and cardiac features distinguishing MIS-C patients within the first 24 hours of admission to the hospital from those who present with similar features but ultimately diagnosed with an alternative etiology. Methods We performed retrospective chart reviews of children (0-20 years) who were admitted to Vanderbilt Children’s Hospital and evaluated under our institutional MIS-C algorithm between June 10, 2020-April 8, 2021. Subjects were identified by review of infectious disease (ID) consults during the study period as all children with possible MIS-C require an ID consult per our institutional algorithm. Clinical, lab, and cardiac characteristics were compared between children with and without MIS-C. The diagnosis of MIS-C was determined by the treating team and available consultants. P-values were calculated using two-sample t-tests allowing unequal variances for continuous and Pearson’s chi-squared test for categorical variables, alpha set at < 0.05. Results There were 128 children admitted with concern for MIS-C. Of these, 45 (35.2%) were diagnosed with MIS-C and 83 (64.8%) were not. Patients with MIS-C had significantly higher rates of SARS-CoV-2 exposure, hypotension, conjunctival injection, abdominal pain, and abnormal cardiac exam (Table 1). Laboratory evaluation showed that patients with MIS-C had lower platelet count, lymphocyte count and sodium level, with higher c-reactive protein, fibrinogen, B-type natriuretic peptide, and neutrophil percentage (Table 2). Patients with MIS-C also had lower ejection fraction and were more likely to have abnormal electrocardiogram. Conclusion We identified early features that differed between patients with MIS-C from those without. Development of a diagnostic prediction model based on these early distinguishing features is currently in progress. Disclosures Natasha B. Halasa, MD, MPH, Genentech (Other Financial or Material Support, I receive an honorarium for lectures - it’s a education grant, supported by genetech)Quidel (Grant/Research Support, Other Financial or Material Support, Donation of supplies/kits)Sanofi (Grant/Research Support, Other Financial or Material Support, HAI/NAI testing) Natasha B. Halasa, MD, MPH, Genentech (Individual(s) Involved: Self): I receive an honorarium for lectures - it’s a education grant, supported by genetech, Other Financial or Material Support, Other Financial or Material Support; Sanofi (Individual(s) Involved: Self): Grant/Research Support, Research Grant or Support James A. Connelly, MD, Horizon Therapeutics (Advisor or Review Panel member)X4 Pharmaceuticals (Advisor or Review Panel member)

821. Changes in Cleaning Practices and Non-conventional Personal Protective Equipment Use due to SARS-CoV-2 and Association with Increases in Multi-drug Resistant Organism Cases

Background During the pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), policy at a Minnesota hospital changed to state that environmental services would not clean rooms of patients with confirmed or suspected SARS-CoV-2 infections, requiring nursing staff to perform these duties. Investigation of a cluster of carbapenem-resistant Enterobacterales (CRE) in patients hospitalized in the same or adjoining rooms on the medical intensive care unit (MICU) raised concern over whether SARS-CoV-2 cleaning practices and non-conventional personal protective equipment (PPE) use led to transmission of multi-drug resistant organisms (MDROs). Methods Infection Prevention conducts passive surveillance for MDRO acquisition in inpatient units. Passive surveillance of SARS-CoV-2 was performed early in the pandemic. Active surveillance SARS-CoV-2 testing on admission was initiated in July 2020 and active surveillance testing for admitted patients every 7 days was initiated in December. Incident cases of vancomycin-resistant Enterococcus (VRE), extended-spectrum-β-lactamase-producing organisms (ESBL), methicillin-resistant S. aureus (MRSA), and CRE were determined for hospitalized patients between March 1, 2020 and February 28, 2021, excluding patients with infection on admission. Rates of hospitalized patients testing positive for SARS-CoV-2 per 100 patient days were compared to rates of patients testing positive for VRE, ESBL, MRSA, and CRE per 100 patient days respectively. The same rate comparisons were completed for the MICU. Using the F-Test Two-Sample to determine variance, the Two-Sample T-test assuming unequal variances was applied to each comparison. Results Correlation was significant between rates of SARS-CoV-2 and VRE (p< 0.005), ESBL (p< 0.005), MRSA (p< 0.005), and CRE (p< 0.005) (Table 1). MICU correlation was significant between rates of SARS-CoV-2 and VRE (p< 0.005), ESBL (p< 0.005), MRSA (p< 0.005), and CRE (p< 0.005) (Table 2). Table 1: Two-sample T-test results assuming unequal variances: Hospital COVID rates per 100 patient days vs. rates of incident positive tests for VRE, ESBL, MRSA, and CRE per 100 patient days Table 2: Two-sample T-test results assuming unequal variances: MICU COVID rates per 100 patient days vs. rates of incident positive tests for VRE, ESBL, MRSA, and CRE per 100 patient days Conclusion The relationships between the rates of SARS-CoV-2 and four MDROs were statistically significant. It can be inferred from this data that changes in hospital cleaning and non-conventional PPE use may have led to an increase in transmission of MDROs in this facility. Disclosures All Authors: No reported disclosures

Relationship Between Nutrition Knowledge and Dietary Intake: An Assessment Among a Sample of Italian Adults

Background: Assessing nutrition knowledge provides useful information especially if coupled with the self-perception of nutrition knowledge that could lead to bias and personal conviction. The objective of this study was to assess nutrition knowledge (NK) and its relationship with eating habits in a group of adults.Methods: A cross-sectional study with the administration of self-reported questionnaires was conducted on a sample of 591 parents (43 ± 5.82 years old) of primary school pupils recruited from the municipality of Rome (urban) and province (rural). The fieldwork was carried out in May 2017. An indicator to evaluate adherence to Italian dietary guidelines was developed. ANOVA (Welch's ANOVA in case of unequal variances) test and chi-squared test were used fixing the significance level at 5% (p < 0.05).Results: The percentage of correct answers to nutrition knowledge was 46%, with the expert recommendation section having the highest percentage (59%). The majority of the respondents (66%) were confident that they had a high level of nutrition knowledge. In 37% of the sample, nutrition knowledge and self-perception nutrition knowledge levels were found to be associated. A total of 40% of the sample showed eating habits congruent with nutrition knowledge level. In the investigated sample, living in rural areas, being young, and having low school education level were factors associated with low nutrition literacy or/and unhealthy eating habits.Conclusions: This study provided a demonstration that an assessment based on a multidimensional and multilevel approach is helpful to identify knowledge gaps and to profile critical segments to put in place targeted policy interventions.

Testing for equality of means with equal and unequal variances

In this paper, we are interested in comparing the conventional t –test with the proposed t – test for testing equality of means with unequal and equal variances. Here, we proposed harmonic mean of variances as an alternative to the pooled sample variance when there is heterogeneity of variances. Two sets of secondary data were obtained from Agricultural Development Project (KWADP) and the Ministry of Agriculture in Ilorin, Kwara State to demonstrate the two test statistics used and the results show that the proposed t – test statistic is found to be appropriate than the conventional t – test statistic when we have unequal variances but the conventional t – test perform better when we have equal variances.

Detecting Geo-Positional Bias in Imagery Collected Using Small UASs

Statistical methods for detecting bias in global positioning system (<small>GPS</small>) error are presented and applied to imagery collected using three common unmanned aerial systems (<small>UASs</small>). Imagery processed without ground control points (<small>GCPs</small>) had horizontal errors of 1.0–2.5 m; however, the errors had unequal variances, significant directional bias, and did not conform to the expected statistical distribution and so should be considered unreliable. When <small>GCPs</small>were used, horizontal errors decreased to less than 5 cm, and the errors had equal variances, directional uniformity, and they conformed to the expected distribution. The analysis identified a longitudinal bias in some of the reference data, which were subsequently excluded from the analysis. Had these data been retained, the estimates of positional accuracy would have been unreliable and inaccurate. These results strongly suggest that examining <small>GPS</small> data for bias should be a much more common practice.

An ACGME-based comparison of neurosurgical and orthopedic resident training in adult spine surgery via a case volume and hours-based analysis

OBJECTIVE In a 2014 analysis of orthopedic and neurological surgical case logs published by the Accreditation Council for Graduate Medical Education (ACGME), it was reported that graduating neurosurgery residents performed more than twice the number of spinal procedures in their training compared with graduating orthopedic residents. There has, however, been no follow-up assessment of this trend. Moreover, whether this gap in case volume equates to a similar gap in procedural hours has remained unstudied. Given the association between surgical volume and outcomes, evaluating the status of this disparity has value. Here, the authors assess trends in case volume and procedural hours in adult spine surgery for graduating orthopedic and neurological surgery residents from 2014 to 2019. METHODS A retrospective analysis of ACGME case logs from 2014 to 2019 for graduating orthopedic and neurological surgery residents was conducted for adult spine surgeries. Case volume was converted to operative hours by using periprocedural times from the 2019 Medicare/Medicaid Physician Fee Schedule. Graduating residents’ spinal cases and hours, averaged over the study period, were compared between the two specialties by using 2-tailed Welch’s unequal variances t-tests (α = 0.05). Longitudinal trends in each metric were assessed by linear regression followed by cross-specialty comparisons via tests for equality of slopes. RESULTS From 2014 to 2019, graduating neurosurgical residents logged 6.8 times as many spinal cases as their orthopedic counterparts, accruing 431.6 (95% CI 406.49–456.61) and 63.8 (95% CI 57.08–70.56) cases (p < 0.001), respectively. Accordingly, graduating neurosurgical residents logged 6.1 times as many spinal procedural hours as orthopedic surgery residents, accruing 1020.7 (95% CI 964.70–1076.64) and 166.6 (95% CI 147.76–185.35) hours (p < 0.001), respectively. Over these 5 years, both fields saw a linear increase in graduating residents’ adult spinal case volumes and procedural hours, and these growth rates were higher for neurosurgery (+16.2 cases/year vs +4.4 cases/year, p < 0.001; +36.4 hours/year vs +12.4 hours/year, p < 0.001). CONCLUSIONS Graduating neurosurgical residents accumulated substantially greater adult spinal case volumes and procedural hours than their orthopedic counterparts from 2014 to 2019. This disparity has been widened by a higher rate of growth in adult spinal cases among neurosurgery residents. Accordingly, targeted efforts to increase spinal exposure for orthopedic surgery residents—such as using cross-specialty collaboration—should be explored.

Trends in physician reimbursements and procedural volumes for radiosurgery versus open surgery in brain tumor care: an analysis of Medicare data from 2009 to 2018

OBJECTIVE Given its minimally invasive nature and effectiveness, stereotactic radiosurgery (SRS) has become a mainstay for the multimodal treatment of intracranial neoplasm. However, no studies have evaluated recent trends in the use of SRS versus those of open resection for the management of brain tumor or trends in the involvement of neurosurgeons in SRS (which is primarily delivered by radiation oncologists). Here, the authors used publicly available Medicare data from 2009 to 2018 to elucidate trends in the treatment of intracranial neoplasm and to compare reimbursements between these approaches. METHODS By using CPT Professional 2019, the authors identified 10 open resection and 9 SRS codes (4 for neurosurgery and 5 for radiation oncology) for the treatment of intracranial neoplasm. Medicare payments (inflation adjusted) and allowed services (number of reimbursed procedures) for each code were abstracted from the Centers for Medicare and Medicaid Services Part B National Summary Data File (2009–2018). Payments per procedure and procedures per 100,000 Medicare enrollees were analyzed with linear regression and compared with tests for equality of slopes (α = 0.05). The average payment per procedure over the study period was compared by using the 2-tailed Welsh unequal variances t-test, and more granular comparisons were conducted by using ANOVA with post hoc Tukey honestly significant difference (HSD) tests. RESULTS From 2009 to 2018, the number of SRS treatments per 100,000 Medicare enrollees for intracranial neoplasm increased by 3.97 cases/year (R2 = 0.99, p < 0.001), while comparable open resections decreased by 0.34 cases/year (R2 = 0.85, p < 0.001) (t16 = 7.5, p < 0.001). By 2018, 2.6 times more SRS treatments were performed per 100,000 enrollees than open resections (74.9 vs 28.7 procedures). However, neurosurgeon involvement in SRS treatment declined over the study period, from 23.4% to 11.5% of SRS treatments; simultaneously, the number of lesions treated per session increased from 1.46 to 1.84 (R2 = 0.98, p < 0.001). Overall, physician payments from 2013 to 2018 averaged $1816.08 (95% CI $1788.71–$1843.44) per SRS treatment and $1565.59 (95% CI $1535.83–$1595.34) per open resection (t10 = 15.9, p < 0.001). For neurosurgeons specifically, reimbursements averaged $1566 per open resection, but this decreased to $1031–$1198 per SRS session; comparatively, radiation oncologists were reimbursed even less (average $359–$898) per SRS session (p < 0.05 according to the Tukey HSD test for all comparisons). CONCLUSIONS Over a decade, the number of open resections for intracranial neoplasm in Medicare enrollees declined slightly, while the number of SRS procedures increased greatly. This latter expansion is largely attributable to radiation oncologists; meanwhile, neurosurgeons have shifted their involvement in SRS toward sessions for the management of multiple lesions.