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Regression-based mediation analysis: a formula for the bias due to an unobserved precursor variable
Kim Steven B.,Lee Joonghak 한국통계학회 2021 Journal of the Korean Statistical Society Vol.50 No.4
Researchers want to know whether the change in an explanatory variable X affects the change in a response variable Y (i.e., X causes Y). In practice, there can be two causal paths from X to Y, the path through a mediating variable M (indirect effect) and the path not through M (direct effect). The parameter estimation and hypothesis testing can be performed by a regression-based mediation model. It is already known that randomization of X is not enough for unbiased estimation, and the bias due to an unobserved variable has been discussed in literature but often overlooked. In this article, we first review the challenge under a simple mediation model, then we provide a formula for the exact bias due to an unobserved precursor variable W, the variable which potentially causes the changes in X, M, and/or Y. We present simulation studies to demonstrate the impact of an unobserved precursor variable on hypothesis testing for indirect effect and direct effect. The simulation results show that the inflation of type I error is serious particularly in a large sample study. To numerically demonstrate the formula of the exact bias, a popular data set published in a journal of statistics education is revisited, and we quantify why the conclusion of data analysis can be different before and after accounting for the precursor variable. The result shall remind the importance of a precursor variable in mediation analysis.
PERFORATION OF THE TEMPOROMANDIBULAR JOINT MENISCUS: DIAGNOSED BY MAGNETIC RESONANCE IMAGING
Kim,Houng Gon,Eward Dolan,James B. Vogler,Steven R. Nokes 大韓顎顔面成形再建外科學會 1989 Maxillofacial Plastic Reconstructive Surgery Vol.11 No.2
Advancement of surgical techniques has made it necessary to accurately diagnose internal derangements. Arthrography and computerized tomography have been used to diagnose the majority of temporomandibular joint disorders, however, these methods have had their disadvantages. Magnetic resonance imaging utilizing surface coils has greatly improved the ability to diagnose meniscus abnormalities without using intrarticular injections or ionizing radiation. Ninety-two patients(184 joints) were evaluated by means of magnetic resonance imaging(MRI). Thirty-on patients (39 joints) were diagnosed as having meniscus perforation. Retrospective review of fifteen patients(20 joints) with a perforated meniscus diagnosed by magnetic resonance imaging pre-operatively demonstrated a sixty-five percent correlation between the radiographic diagnosis and the surgical findings.
Lee, B.C.,Kim, M.S.,Pae, M.,Yamamoto, Y.,Eberle, D.,Shimada, T.,Kamei, N.,Park, H.S.,Sasorith, S.,Woo, J.,You, J.,Mosher, W.,Brady, Hugh J.M.,Shoelson, Steven E.,Lee, J. Cell Press 2016 Cell metabolism Vol.23 No.4
<P>Obesity-induced inflammation mediated by immune cells in adipose tissue appears to participate in the pathogenesis of insulin resistance. We show that natural killer (NK) cells in adipose tissue play an important role. High-fat diet (HFD) increases NK cell numbers and the production of proinflammatory cytokines, notably TNF alpha, in epididymal, but not subcutaneous, fat depots. When NK cells were depleted either with neutralizing antibodies or genetic ablation in E4bp4(+/-) mice, obesity-induced insulin resistance improved in parallel with decreases in both adipose tissue macrophage (ATM) numbers, and ATM and adipose tissue inflammation. Conversely, expansion of NK cells following IL-15 administration or reconstitution of NK cells into E4bp4(-/-) mice increased both ATM numbers and adipose tissue inflammation and exacerbated HFD-induced insulin resistance. These results indicate that adipose NK cells control ATMs as an upstream regulator potentially by producing proinflammatory mediators, including TNF alpha, and thereby contribute to the development of obesity-induced insulin resistance.</P>
Ultra Fast Flash Observatory to observe the prompt photons from Gamma Ray Bursts
Jiwoo Nam,Steven Boggs,G. Ripov,Bruce Grossan,Jin-A Jeon,Joo-Young Jin,Ae-Ra Jung,Ji-Eun Kim,Minsoo Kim,Yong-Kweon Kim,P. Klimov,B. Khrenov,Chang-hwan Lee,Jik Lee,Go-Woon Na,Shin-Woo Nam,Il-Heung Park 한국천문학회 2009 天文學會報 Vol.34 No.1
( W. Ray Kim ),( Eric J. Lawitz ),( Peter Ruane ),( Catherine Stedman ),( Graham Foster ),( Robert H. Hyland ),( Sarah Coogan ),( Stephanie Moody ),( Hadas Dvory-sobo ),( Steven J. Knox ),( Diana M. B 대한간학회 2016 춘·추계 학술대회 (KASL) Vol.2016 No.1
Aims: Significant advances in the treatment of chronic hepatitis C have been made with direct acting antiviral (DAA) regimens. While SVR rates may now be achieved in the majority of patients, data describing long-term virologic and clinical outcomes with these regimens are needed. Methods: We report interim data from two 3-year registry studies capturing long-term outcomes in patients with chronic hepatitis C treated with DAAs. Subjects are enrolled into two registries according to SVR status; SVR (SVR registry) versus non-SVR (Sequence registry). We determined the durability of SVR, relapse and reinfection rates. The persistence of resistance associated variants (RAVs) in treatment failures is followed. Liver disease progression is assessed by periodic clinical & labroratory evaluations. Results: 5433 patients enrolled in the SVR registry with a median (range) follow-up of 71 (0-156) weeks. 536 patients enrolled in the Sequence registry with a median (range) of follow-up of 44 (0-159) weeks. Demographic and disease characteristics are described below. In the SVR registry, at the time of data analysis, 99.7% (5414/5433) of patients have maintained SVR with 0.3% (19/5433) having emergent virus (6 relapses, 8 new infections, 5 to be confirmed). Viral emergence occurred by Week 96 in all patients. In the Sequence registry of 89 patients who received an NS5A inhibitor and had baseline sequencing data, 91.0% (81/89) had NS5A RAVs at Week 96. HCC was reported in 0.3% (16/5433) and 0.9% (5/536) of patients in the SVR and Sequence registries through Week 96 respectively. There were no significant changes in laboratory evaluations or liver disease assessments. Conclusions: SVR achieved following treatment with DAA regimens is durable. In patients failing NS5A-containing regimens, treatment- emergent NS5A RAVs persist. Rates of clinical disease progression and HCC are low. Ongoing reporting from these registry studies will be required to confirm these findings.
Jo Jung Su,Kim Dong Sub,Jo Won Jun,Sim Ha Seon,Lee Hye Jin,Moon Yu Hyun,Woo Ui Jeong,Jung Soo Bin,Kim Steven B.,Mo Xiaoming,Ahn Su Ran,Kim Sung Kyeom 한국원예학회 2022 Horticulture, Environment, and Biotechnology Vol.63 No.4
The strawberry growth and fruit yield of five Korean cultivars in the tunnel-type greenhouse predicted using their growth. The number of leaves, petiole length, leaf length and width, crown diameter, and the ratio of red and far-red (RFR) of the five Korean cultivars were measured during the cultivation period. The number of leaves of all cultivars exhibited a similar trend during this period; the plant and petiole length of ‘Maehyang’ were the longest, leaf length exhibited similar trends in all five cultivars except for ‘Jukhyang’, the leaf width of ‘Arihyang’, was the longest, and crown diameter of ‘Keumsil’ was the thickest. The leaf length, crown diameter, and RFR were associated with the fruit yield in the multiple linear regression. When a single model was used to predict the yield of all five cultivars, the correlation between expected yield and actual yield was r = 0.53. When cultivar-specific models were built for the prediction, the correlation increased to r = 0.77. The results indicated that the fruit yield of strawberry cultivars could be better predicted by considering cultivar-specific information, so it may be necessary to consider individual cultivars specifically rather than all cultivars simultaneously.
Ultra Fast Flash Observatory to observe the prompt photons from Gamma Ray Bursts
Nam, Ji-Woo,Boggs, Steven,Ripov, G.,Grossan, Bruce,Jeon, Jin-A,Jin, Joo-Young,Jung, Ae-Ra,Kim, Ji-Eun,Kim, Min-Soo,Kim, Yong-Kweon,Klimov, P.,Khrenov, B.,Lee, Chang-Hwan,Lee, Jik,Na, Go-Woon,Nam, Shin 한국우주과학회 2009 한국우주과학회보 Vol.18 No.1
Cho, Soongwon,Kang, Dong-Ku,Sim, Steven,Geier, Florian,Kim, Jin-Young,Niu, Xize,Edel, Joshua B.,Chang, Soo-Ik,Wootton, Robert C. R.,Elvira, Katherine S.,deMello, Andrew J. American Chemical Society 2013 ANALYTICAL CHEMISTRY - Vol.85 No.18
<P>We present a fully integrated droplet-based microfluidic platform for the high-throughput assessment of photodynamic therapy photosensitizer (PDT) efficacy on <I>Escherichia coli</I>. The described platform is able to controllably encapsulate cells and photosensitizer within pL-volume droplets, incubate the droplets over the course of several days, add predetermined concentrations of viability assay agents, expose droplets to varying doses of electromagnetic radiation, and detect both live and dead cells online to score cell viability. The viability of cells after encapsulation and incubation is assessed in a direct fashion, and the viability scoring method is compared to model live/dead systems for calibration. Final results are validated against conventional colony forming unit assays. In addition, we show that the platform can be used to perform concurrent measurements of light and dark toxicity of the PDT agents and that the platform allows simultaneous measurement of experimental parameters that include dark toxicity, photosensitizer concentration, light dose, and oxygenation levels for the development and testing of PDT agents.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancham/2013/ancham.2013.85.issue-18/ac4022067/production/images/medium/ac-2013-022067_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ac4022067'>ACS Electronic Supporting Info</A></P>
Subseasonal Prediction of Wintertime East Asian Temperature Based on Atmospheric Teleconnections
Yoo, Changhyun,Johnson, Nathaniel C.,Chang, Chueh-Hsin,Feldstein, Steven B.,Kim, Young-Ha American Meteorological Society 2018 Journal of climate Vol.31 No.22
<P> A composite-based statistical model utilizing Northern Hemisphere teleconnection patterns is developed to predict East Asian wintertime surface air temperature for lead times out to 6 weeks. The level of prediction is determined by using the Heidke skill score. The prediction skill of the statistical model is compared with that of hindcast simulations by a climate model, Global Seasonal Forecast System, version 5. When employed individually, three teleconnections (i.e., the east Atlantic/western Russian, Scandinavian, and polar/Eurasian teleconnection patterns) are found to provide skillful predictions for lead times beyond 4-5 weeks. When information from the teleconnections and the long-term linear trend are combined, the statistical model outperforms the climate model for lead times beyond 3 weeks, especially during those times when the teleconnections are in their active phases. </P>