Category: Statistics

J Opt Soc Am A Opt Image Sci Vis. 2021 May 1;38(5):654-662. doi: 10.1364/JOSAA.412972.

ABSTRACT

In previous studies, the receivers in indoor visible light communication (VLC) were usually fixed. However, in reality, the receivers in VLC have random locations and orientations. Therefore, it is important to consider these random factors for performance analysis in VLC. In this paper, we consider a typical VLC system with a fixed transmitter and a random receiver. Two types of receivers are investigated: (1) those with random location and (2) those with random orientation. Based on the established system model, the statistical characteristics of the channel were obtained, and closed-form expressions of the average channel capacity and the outage probability were derived, respectively. Finally, numerical results verified the accuracy of derived theoretical expressions. Moreover, the effects of the nominal optical intensity, the dimming target, the transmitter height, the receiver zone’s radius, the outage threshold, and the Lambertian emission order on system performance were also provided.

PMID:33983270 | DOI:10.1364/JOSAA.412972

Appl Opt. 2021 May 1;60(13):3936-3946. doi: 10.1364/AO.419594.

ABSTRACT

We discuss various methods for acquiring optical links in space using a dedicated acquisition sensor. Statistical models are developed and simple analytical equations derived that compare the performance between a single- and dual-spiral scan approach as well as between sequential and parallel acquisition of link chains. Simple derived analytical equations allow relating essential search parameters such as track width, variance of the uncertainty distribution, capture radius, and scan speed to the probabilities of acquiring the links within a specific time. We also assess the probability of failing to acquire a link due to beam jitter and derive a simple analytical model that allows determining the maximum tolerable jitter for a given beam overlap and required probability of success. All results are validated by Monte Carlo simulations and applied to the concrete example of the GRACE FO mission.

PMID:33983332 | DOI:10.1364/AO.419594

Appl Opt. 2021 May 10;60(14):4154-4164. doi: 10.1364/AO.419746.

ABSTRACT

The LiDAR sensor has been widely used for reconstruction in urban scenes. However, the current registration method makes it difficult to find stable 3D point correspondences from sparse and low overlapping LiDAR point clouds. In the urban situation, most of the LiDAR point clouds have a common flat ground. Therefore, we propose a novel, to the best of our knowledge, multi-level height (MH) maps-based coarse registration method. It requires that source and target point clouds have a common flat ground, which is easily satisfied for LiDAR point clouds in urban scenes. With MH maps, 3D registration is simplified as 2D registration, increasing the speed of registration. Robust correspondences are extracted in MH maps with different height intervals and statistic height information, improving the registration accuracy. The solid-state LiDAR Livox Mid-100 and mechanical LiDAR Velodyne HDL-64E are used in real-data and dataset experiments, respectively. Verification results demonstrate that our method is stable and outperforms state-of-the-art coarse registration methods for the sparse case. Runtime analysis shows that our method is faster than these methods, for it is non-iterative. Furthermore, our method can be extended for the unordered multi-view point clouds.

PMID:33983168 | DOI:10.1364/AO.419746

Appl Opt. 2021 Apr 10;60(11):3257-3265. doi: 10.1364/AO.417344.

ABSTRACT

This paper continues a series of studies on using underwater solar path imagery (USPI) to retrieve characteristics of wind-driven waves and their variations in the field of near-surface hydrophysical processes under the influence of surfactant films. Research is based on previously developed mathematical models of USPI and its statistical moments, the Elfouhaily spectrum of wind-driven waves, the Ermakov model of wave damping by a thin film, and the Cox-Munk result for a thick oil film. A high sensitivity of two statistical moments of USPI to variations of wind-wave conditions and viscoelastic characteristics of oil films was shown. The presented examples demonstrated 20%-40% narrowing of the statistically average image (the first statistical moment) for thin films and more than 2 times narrowing for thick films. The film presence also leads to significant changes in the autocorrelation function of USPI. The characteristic scales and magnitudes of changes in the considered statistical moments fit into the ranges of values that can be recorded in practice using even inexpensive video cameras. At the same time, there are cases in which these moments are close. For example, for a clean sea surface in weak winds and for a surface covered by a thin film in stronger winds. These cases can be distinguished by analyzing a series of instant images. As an example, a series of real underwater images demonstrating changes in the glint structure with the surfactant film spot passing through the observed sea surface area were analyzed. This example is intended to help researchers to distinguish cases of wind weakening and a surfactant film presence.

PMID:33983227 | DOI:10.1364/AO.417344

Br J Neurosurg. 2021 May 13:1-5. doi: 10.1080/02688697.2021.1923651. Online ahead of print.

ABSTRACT

BACKGROUND AND OBJECTIVES: Understanding the biomechanical relationship between the spine and the pelvis is important for the management of symptomatic lumbar disease. There are several different metrics that may be used to evaluate the spine in the sagittal plane. The aim of this study is to compare spinopelvic parameters and global sagittal angle (GSA) in a cohort of patients with upper lumbar disc herniations (ULDH) to identify a correlation between the pelvic incidence (PI) and GSA with ULDH.

MATERIAL AND METHODS: Eighty-six patients with ULDH and 86 asymptomatic control group underwent whole body biplanar stereographs- and magnetic resonance imaging . The spinopelvic parameters and GSA were measured.

RESULTS: PI, sacral slope (SS), lumbar lordosis (LL), and thoracic kyphosis (TK) were all significantly lower than in the control group (p < 0.01) but there was no difference in the pelvic tilt (PT). The two groups were divided into subgroups. PI in the T12-L1 and L1-L2 level groups were significantly smaller than in the control group (p < 0.05). Also, there was a significant difference in TK and LL between the L3-L4 level and control group (p < 0.05), but there was no statistically significant difference in PT between all levels and the control group.

CONCLUSION: This study demonstrated a unique correlation between several spinopelvic parameters and GSA and the occurrence of ULDH. Lower PI, SS, and LL in T12-L1 and L1-L2 levels indicates a flat lumbar spine which may increase mechanical stress at these levels, thereby leading to disc herniation.

PMID:33983097 | DOI:10.1080/02688697.2021.1923651

Glob Health Action. 2021 Jan 1;14(1):1890929. doi: 10.1080/16549716.2021.1890929.

ABSTRACT

Background: The perception within literature and populace is that the private for-profit sector is for the rich only, and this characteristic results in behaviours that hinder advancement of Universal health coverage (UHC) goals. The context of Northern Uganda presents an opportunity for understanding how the private sector continues to thrive in settings with high poverty levels and history of conflict.Objective: The study aimed at understanding access mechanisms employed by the formal private for-profit providers (FPFPs) to enable pro-poor access to health services in post conflict Northern Uganda.Methods: Data collection was conducted in Gulu municipality in 2015 using Organisational survey of 45 registered formal private for-profit providers (FPFPs),10 life histories, and 13 key informant interviews. Descriptive statistics were generated for the quantitative findings whereas qualitative findings were analysed thematically.Results: FPFPs pragmatically employed various access mechanisms and these included fee exemptions and provision of free services, fee reductions, use of loan books, breaking down doses and partial payments. Most mechanisms were preceded by managers’ subjective identification of the poor, while operationalisation heavily depended on the managers’ availability and trust between the provider and the customer. For a few FPFPs, partnerships with Non-governmental organisations (NGOs) and government enabled provision of free, albeit mainly preventive services, including immunisation, consultations, screening for blood pressure and family planning. Challenges such as quality issues, information asymmetry and standardisation of charges arose during implementation of the mechanisms.Conclusion: The identification of the poor by the FPFPs was subjective and unsystematic. FPFPs implemented various innovations to ensure pro-poor access to health services. However, they face a continuous dilemma of balancing the profit maximization and altruism objectives. Implementation of some pro-poor mechanisms raises concerns included those related to quality and standardisation of pricing.

PMID:33983106 | DOI:10.1080/16549716.2021.1890929

JMIR Med Educ. 2021 May 13;7(2):e28805. doi: 10.2196/28805.

ABSTRACT

BACKGROUND: Health professions students use social media to communicate with other students and health professionals, discuss career plans or coursework, and share the results of research projects or new information. These platforms allow students to share thoughts and perceptions that are not disclosed in formal education settings. Twitter provides an excellent window through which health professions educators can observe students’ sociocultural and learning needs. However, despite its merits, cyberincivility on Twitter among health professions students has been reported. Cyber means using electronic technologies, and incivility is a general term for bad manners. As such, cyberincivility refers to any act of disrespectful, insensitive, or disruptive behavior in an electronic environment.

OBJECTIVE: This study aims to describe the characteristics and instances of cyberincivility posted on Twitter by self-identified health professions students. A further objective of the study is to analyze the prevalence of tweets perceived as inappropriate or potentially objectionable while describing patterns and differences in the instances of cyberincivility posted by those users.

METHODS: We used a cross-sectional descriptive Twitter data mining method to collect quantitative and qualitative data from August 2019 to February 2020. The sample was taken from users who self-identified as health professions students (eg, medicine, nursing, dental, pharmacy, physician assistant, and physical therapy) in their user description. Data management and analysis were performed with a combination of SAS 9.4 for descriptive and inferential statistics, including logistic regression, and NVivo 12 for descriptive patterns of textual data.

RESULTS: We analyzed 20 of the most recent tweets for each account (N=12,820). A total of 639 user accounts were analyzed for quantitative analysis, including 280 (43.8%) medicine students and 329 (51.5%) nursing students in 22 countries: the United States (287/639, 44.9%), the United Kingdom (197/639, 30.8%), unknown countries (104/639, 16.3%), and 19 other countries (51/639, 8.0%). Of the 639 accounts, 193 (30.2%) were coded as having instances of cyberincivility. Of these, 61.7% (119/193), 32.6% (63/193), and 5.7% (11/193) belonged to students in nursing, medicine, and other disciplines, respectively. Among 502 instances of cyberincivility identified from 641 qualitative analysis samples, the largest categories were profanity and product promotion. Several aggressive or biased comments toward other users, politicians, or certain groups of people were also found.

CONCLUSIONS: Cyberincivility is a multifaceted phenomenon that must be considered in its complexity if health professions students are to embrace a culture of mutual respect and collaboration. Students’ perceptions and reports of their Twitter experiences offer insights into behavior on the web and the evolving role of cyberspace, and potentially problematic posts provide opportunities for teaching digital professionalism. Our study indicates that there is a continued need to provide students with guidance and training regarding the importance of maintaining a professional persona on the web.

PMID:33983129 | DOI:10.2196/28805

J Urol. 2021 May 13:101097JU0000000000001844. doi: 10.1097/JU.0000000000001844. Online ahead of print.

ABSTRACT

PURPOSE: We investigated 2019 and 2020 US News and World Report (USNWR) methodologies of assessing pediatric urology surgical revision rates for distal hypospadias, pyeloplasty, and ureteral reimplantation to evaluate statistical power and misclassification risks.

METHODS: Median annual volumes of distal hypospadias, pyeloplasty, and ureteral reimplantation procedures by hospital from 2016-2018 were calculated using the Pediatric Health Information Systems database. USNWR 2019 and 2020 methodologies were assessed to calculate power required to detect differences between hospitals and risk of hospital misclassifications.

RESULTS: Median (IQR) annual hospital procedure volume was 72 (43-97) for distal hypospadias procedures, 19 (9-34) for pyeloplasties, and 35 (19-50) for ureteral reimplantations. Based on 2019 methodology, in order to achieve 80% power 764 cases/hospital are required to distinguish between a 1% vs. 3% surgical revision rate, 1,500 cases/hospital are required to distinguish between a 3% vs. 5% revision rate, and 282 cases/hospital are required to distinguish between a 1% vs. 5% revision rate. Based on 2020 methodology, 98.0% of hospitals do not have adequate ureteral reimplantation volume to achieve full points even when reporting no revisions; similarly, 66.0% do not have adequate pyeloplasty volume, and 10.9% do not have adequate distal hypospadias volume. Risks of misclassification exceed 50% in several instances among hospitals reporting distal hypospadias and pyeloplasty revisions using both 2019 and 2020 methodology.

CONCLUSIONS: Based on median-volume hospitals, current USNWR methods for classifying revision rates for distal hypospadias, pyeloplasty, and ureteral reimplantation have insufficient power and are at high risk for misclassification.

PMID:33983039 | DOI:10.1097/JU.0000000000001844

J Vasc Access. 2021 May 13:1129729820976260. doi: 10.1177/1129729820976260. Online ahead of print.

ABSTRACT

PURPOSE: To review the incidence and type of tunneled hemodialysis catheter (THC) complications in a large cohort of patients with end-stage renal disease. Additionally, the longevity of the THC and factors predicting high risk for catheter complications were assessed.

MATERIAL AND METHODS: Between August 2009 and December 2016, a cohort of 538 patients underwent primary THC insertion; in 119 patients, THC was inserted after failed arteriovenous fistula or graft. Patients without available clinical follow-up data (n = 67) were excluded for further analysis. The Charlson comorbidity index (CCI) was calculated for each patient. The cumulative incidence function (CIF) was used for THC overall longevity, while Cox proportional hazards models were used for risk factor analysis.

RESULTS: In 352 patients, THC was inserted in a virgin neck. THC-related complications were observed in n = 104 (29.55%) of the patients. Infection occurred in n = 38 (10.80%) and malfunction, related to thrombosis or mechanical damage, in n = 45 (12.78%). Removal of the THC for the purpose of switching to alternative dialysis methods was planned in n = 135 (38.4%). The remaining patients were still alive with a functioning THC (n = 18; 5.11%) or died (n = 95; 27%) with a functioning THC. The THC survival rate was 82.67%, 78.13%, 74.15%, 72.96%, 71.02%, and 70.63% on follow-up after 6 months, and after 1-5 years, respectively. Gender, CCI, age, and site of placement of the catheter were found not to affect the life of the catheter.

CONCLUSION: The overall complication rate in primary inserted THC was nearly 30% and mainly related to infection and malfunction. THC survival was more than 70% after 5 years, which supports its use for permanent dialysis access, irrespective of gender, CCI, age, and jugular side of THC placement.

PMID:33983083 | DOI:10.1177/1129729820976260

J Sex Res. 2021 May 13:1-12. doi: 10.1080/00224499.2021.1924606. Online ahead of print.

ABSTRACT

Accurate, reliable self-reports of sexual behavior are a crucial component of valid HIV risk-estimation and behavioral intervention evaluation, yet this data’s reliability remains understudied. The goal of this study was to describe interpartner agreement on recent receptive anal intercourse (AI) and condomless receptive AI frequencies, among a sample of male couples. We quantified interpartner agreement on self-reported receptive AI and condomless receptive AI (absolute and relative to AI frequency), and position and condom use during a couple’s most recent AI, using cross-sectional data from male partners (US, 2016-2017; N = 718 individuals). Proportional and statistical agreement (intraclass correlation coefficients (ICC), kappa (k)) were assessed. Observed agreement for receptive AI frequency was 49.44% (ICC (95% CI): 0.82(0.79, 0.84)) and for relative receptive frequency, 59.05% (ICC: 0.96 (0.85, 0.96). Agreement on condomless receptive AI was 90.21% (ICC: 0.78 (0.75, 0.82), and for relative condomless receptive AI, 91.15% (ICC: 0.80 (0.77, 0.83). Most recent AI position agreement was 89.42% (k (95% CI): 0.84 (0.80, 0.88)), and condom use, 98.89% (k: 0.82 (0.87, 0.98)). Observed agreement was higher among those who reported consistent positioning and condom use. Further research on self-reported sexual behavior data is needed to improve research validity and intervention effectiveness.

PMID:33983091 | DOI:10.1080/00224499.2021.1924606