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Judith Lok, Ph.D.

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My research focuses on the development and application of causal inference statistical methods for problems in HIV/AIDS research, with a special focus on the effects of highly active antiretroviral treatment, HAART. I have established strong productive interest in this area with important theoretical contributions in Statistica Neerlandica, the Scandinavian Journal of Statistics, the Annals of Statistics, Biometrics, and Biostatistics. I have a strong record in the application of novel causal inference methods to longitudinal observational studies of HIV-positive patients. For example, (1) I have analyzed the risk of cardiovascular outcomes associated with Abacavir use [Ribaudo et al., CID 2011]. For this project, we have applied Marginal Structural Models. (2) I have investigated the impact of age on the prognostic capacity of CD8+ T-cell activation during suppressive antiretroviral therapy [Lok et al., AIDS 2013, and Schnitzer et al., accepted by Biostatistics]. For this project, we have developed doubly robust, optimal estimators for a prediction model for the probability of an event occurring at or before a pre-specified point in time. (3) In collaboration with Kiragga and Yiannoutsos, I have estimated the CD4 count trajectory adjusting for dropout among HIV-positive patients receiving HAART in an East African HIV care center [Kiragga et al, JAIDS 2014]. Extra complication in this latter analysis was that dropout from this cohort depends on the survival status of the patients at the time of the first missed visit, as became apparent from data collected from patients after they dropped out of the study. (4) I have introduced “organic” direct and indirect effects, aiming to estimate how much of the effect of a treatment is mediated by a covariate that cannot be “set” to any specific value [Lok, submitted to Statistics in Medicine]. (5) I have developed a new class of Structural Nested Mean Models to evaluate the impact of timing of starting treatment following infection. I have applied this to investigate the impact of time between infection and HAART initiation on immune reconstitution in early-stage HIV-positive patients [Lok et al., Biometrics 2012]. (6) We have applied Inverse Probability of Censoring Weighting to investigate factors associated with remaining on initial randomized efavirenz-containing regimens [Smurzynski et al, AIDS 2013]. (7) I have evaluated the long-term CD4 count trajectory under HAART of HIV-positive patients in the US, additionally evaluating what the CD4 trajectory might have been had some patients not discontinued antiretroviral therapy when their CD4 counts increased to high levels (reflecting treatment management practices at the time) [Lok et al., AIDS 2010].

The research activities and funding listed below are automatically derived from NIH ExPORTER and other sources, which might result in incorrect or missing items. Faculty can login to make corrections and additions.
  1. R01AI100762 (LOK, JUDITH JACQUELINE) Mar 19, 2012 - Feb 29, 2016
    Methods to find and model predictors of the causal effect of HAART
    Role: Principal Investigator

Publications listed below are automatically derived from MEDLINE/PubMed and other sources, which might result in incorrect or missing publications. Faculty can login to make corrections and additions.
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  1. Evans SR, Follmann D, Liu Y, Holland T, Doernberg SB, Rouphael N, Hamasaki T, Jiang Y, Lok JJ, Tran TTT, Harris AD, Fowler VG, Boucher H, Kreiswirth BN, Bonomo RA, Van Duin D, Paterson DL, Chambers H. Sequential, Multiple-Assignment, Randomized Trials for COMparing Personalized Antibiotic StrategieS (SMART-COMPASS). Clin Infect Dis. 2019 May 17; 68(11):1961-1967. PMID: 30351426.
    Citations:    Fields:    
  3. van Duin D, Lok JJ, Earley M, Cober E, Richter SS, Perez F, Salata RA, Kalayjian RC, Watkins RR, Doi Y, Kaye KS, Fowler VG, Paterson DL, Bonomo RA, Evans S. Colistin Versus Ceftazidime-Avibactam in the Treatment of Infections Due to Carbapenem-Resistant Enterobacteriaceae. Clin Infect Dis. 2018 01 06; 66(2):163-171. PMID: 29020404.
    Citations: 11     Fields:    
  4. Erlandson KM, Kitch D, Wester CW, Kalayjian RC, Overton ET, Castillo-Mancilla J, Koletar SL, Benson CA, Campbell TB, Robertson K, Lok JJ. The Impact of Statin and Angiotensin-Converting Enzyme Inhibitor/Angiotensin Receptor Blocker Therapy on Cognitive Function in Adults With Human Immunodeficiency Virus Infection. Clin Infect Dis. 2017 Nov 29; 65(12):2042-2049. PMID: 29020174.
    Citations:    Fields:    Translation:HumansCellsCTClinical Trials
  6. Huvane J, Komarow L, Hill C, Tran TT, Pereira C, Rosenkranz SL, Finnemeyer M, Earley M, Jiang HJ, Wang R, Lok J, Evans SR. Fundamentals and Catalytic Innovation: The Statistical and Data Management Center of the Antibacterial Resistance Leadership Group. Clin Infect Dis. 2017 Mar 15; 64(suppl_1):S18-S23. PMID: 28350899.
    Citations: 5     Fields:    Translation:Humans
  7. Lok JJ, Yang S, Sharkey B, Hughes MD. Estimation of the cumulative incidence function under multiple dependent and independent censoring mechanisms. Lifetime Data Anal. 2018 04; 24(2):201-223. PMID: 28238045.
    Citations:    Fields:    
  8. Yang S, Lok JJ. A goodness-of-fit test for structural nested mean models. Biometrika. 2016 09; 103(3):734-741. PMID: 27980344.
    Citations:    Fields:    
  9. Lok JJ. Defining and estimating causal direct and indirect effects when setting the mediator to specific values is not feasible. Stat Med. 2016 09 30; 35(22):4008-20. PMID: 27229743.
    Citations:    Fields:    Translation:Humans
  10. Schnitzer ME, Lok JJ, Gruber S. Variable Selection for Confounder Control, Flexible Modeling and Collaborative Targeted Minimum Loss-Based Estimation in Causal Inference. Int J Biostat. 2016 05 01; 12(1):97-115. PMID: 26226129.
    Citations: 3     Fields:    Translation:Humans
  11. Lok JJ, Hughes MD. Evaluating predictors of competing risk outcomes when censoring depends on time-dependent covariates, with application to safety and efficacy of HIV treatment. Stat Med. 2016 06 15; 35(13):2183-94. PMID: 26763556.
    Citations:    Fields:    Translation:Humans
  12. Schnitzer ME, Lok JJ, Bosch RJ. Double robust and efficient estimation of a prognostic model for events in the presence of dependent censoring. Biostatistics. 2016 Jan; 17(1):165-77. PMID: 26224070.
    Citations: 1     Fields:    Translation:Humans
  13. Kiragga AN, Lok JJ, Musick BS, Bosch RJ, Mwangi A, Wools-Kaloustian KK, Yiannoutsos CT. CD4 trajectory adjusting for dropout among HIV-positive patients receiving combination antiretroviral therapy in an East African HIV care centre. J Int AIDS Soc. 2014; 17:18957. PMID: 25131801.
    Citations: 4     Fields:    Translation:HumansCells
  14. Lok JJ, Hunt PW, Collier AC, Benson CA, Witt MD, Luque AE, Deeks SG, Bosch RJ. The impact of age on the prognostic capacity of CD8+ T-cell activation during suppressive antiretroviral therapy. AIDS. 2013 Aug 24; 27(13):2101-10. PMID: 24326304.
    Citations: 10     Fields:    Translation:HumansCells
  15. Smurzynski M, Wu K, Schouten JT, Lok JJ, Bosch RJ, Taiwo B, Johnson VA, Collier AC. Factors associated with remaining on initial randomized efavirenz-containing regimens. AIDS. 2013 Jul 31; 27(12):1887-97. PMID: 23925417.
    Citations:    Fields:    Translation:Humans
  16. Lok JJ, DeGruttola V. Impact of time to start treatment following infection with application to initiating HAART in HIV-positive patients. Biometrics. 2012 Sep; 68(3):745-54. PMID: 22352840.
    Citations: 2     Fields:    Translation:Humans
  17. Ribaudo HJ, Benson CA, Zheng Y, Koletar SL, Collier AC, Lok JJ, Smurzynski M, Bosch RJ, Bastow B, Schouten JT. No risk of myocardial infarction associated with initial antiretroviral treatment containing abacavir: short and long-term results from ACTG A5001/ALLRT. Clin Infect Dis. 2011 Apr 01; 52(7):929-40. PMID: 21427402.
    Citations: 43     Fields:    Translation:Humans
  18. Lok JJ, Bosch RJ, Benson CA, Collier AC, Robbins GK, Shafer RW, Hughes MD. Long-term increase in CD4+ T-cell counts during combination antiretroviral therapy for HIV-1 infection. AIDS. 2010 Jul 31; 24(12):1867-76. PMID: 20467286.
    Citations: 31     Fields:    Translation:HumansCells
  19. van der Linden YM, Lok JJ, Steenland E, Martijn H, van Houwelingen H, Marijnen CA, Leer JW. Single fraction radiotherapy is efficacious: a further analysis of the Dutch Bone Metastasis Study controlling for the influence of retreatment. Int J Radiat Oncol Biol Phys. 2004 Jun 01; 59(2):528-37. PMID: 15145173.
    Citations: 49     Fields:    Translation:HumansCTClinical Trials
  20. Van der Linden YM, Dijkstra PD, Kroon HM, Lok JJ, Noordijk EM, Leer JW, Marijnen CA. Comparative analysis of risk factors for pathological fracture with femoral metastases. J Bone Joint Surg Br. 2004 May; 86(4):566-73. PMID: 15174555.
    Citations: 27     Fields:    Translation:Humans
  21. van der Peijl ID, Vliet Vlieland TP, Versteegh MI, Lok JJ, Munneke M, Dion RA. Exercise therapy after coronary artery bypass graft surgery: a randomized comparison of a high and low frequency exercise therapy program. Ann Thorac Surg. 2004 May; 77(5):1535-41. PMID: 15111138.
    Citations: 7     Fields:    Translation:HumansCTClinical Trials
  22. van der Linden YM, Kroon HM, Dijkstra SP, Lok JJ, Noordijk EM, Leer JW, Marijnen CA. Simple radiographic parameter predicts fracturing in metastatic femoral bone lesions: results from a randomised trial. Radiother Oncol. 2003 Oct; 69(1):21-31. PMID: 14597353.
    Citations: 13     Fields:    Translation:HumansCTClinical Trials
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Funded by the NIH National Center for Advancing Translational Sciences through its Clinical and Translational Science Awards Program, grant number UL1TR002541.