Five Things You Should Not Use Blockchain For

The Bitcoin fever notwithstanding, the underlying blockchain technology cannot solve all data exchange and product needs, as some seem to believe. This paper provides examples of problems that we believe are poorly suited to a blockchain solution.acceptedVersio

A Tertiary Review on Blockchain and Sustainability With Focus on Sustainable Development Goals

Sustainable development is crucial to securing the future of humanity. Blockchain as a disruptive technology and a driver for social change has exhibited great potential to promote sustainable practices and help organizations and governments achieve the United Nations’ Sustainable Development Goals (SDGs). Existing literature reviews on blockchain and sustainability often focus only on topics related to a few SDGs. There is a need to consolidate existing results in terms of SDGs and provide a comprehensive overview of the impacts that blockchain technology may have on each SDG. This paper intends to bridge this gap, presenting a tertiary review based on 42 literature reviews, to investigate the relationship between blockchain and sustainability in light of SDGs. The method used is a consensus-based expert elicitation with thematic analysis. The findings include a novel and comprehensive mapping of impact-based interlinkage of blockchain and SDGs and a systematic overview of drivers and barriers to adopting blockchain for sustainability. The findings reveal that blockchain can have a positive impact on all 17 SDGs though some negative effects can occur and impede the achievement of certain objectives. 76 positive and 10 negative linkages between blockchain adoption and the 17 SDGs as well as 45 factors that drive or hinder blockchain adoption for the achievement of SDGs have been identified. Research gaps to overcome the barriers and enhance blockchain’s positive impacts have also been identified. The findings may help managers in evaluating the applicability and tradeoffs, and policymakers in making supportive measures to facilitate sustainability using blockchain.publishedVersio

High-Performance Asynchronous Byzantine Fault Tolerance Consensus Protocol

In response to new and innovating blockchain-based systems with Internet of Things (IoT), there is a need for consensus mechanisms that can provide high transaction throughput and security, despite varying network quality. Honeybadger was the first practical, asynchronous Byzantine Fault Tolerance (BFT) consensus protocol, achieving high scalability and robustness without making any timing assumptions regarding the network. To improve the current asynchronous consensus protocols, we designed Asynchronous Byzantine Fault Tolerance (ABFT) consensus protocol through integrating threshold Elliptic Curve Digital Signature Algorithm (ECDSA) signatures and optimization of erasure coding parameters, as well as additional implementation-level optimizations. We implement a prototype of ABFT, and evaluate its performance at scale in a global WAN network and a network affected by asymmetric network degradation. Our results show that ABFT provides considerably higher performance, significantly lower computational overhead, and greater scalability than its predecessors. ABFT can reach up to 38.700 transactions per second in throughput. Furthermore, we empirically show that ABFT is unaffected by asymmetric network degradation within the fault threshold.acceptedVersio

Non-intersecting Brownian walkers and Yang-Mills theory on the sphere

We study a system of N non-intersecting Brownian motions on a line segment [0,L] with periodic, absorbing and reflecting boundary conditions. We show that the normalized reunion probabilities of these Brownian motions in the three models can be mapped to the partition function of two-dimensional continuum Yang-Mills theory on a sphere respectively with gauge groups U(N), Sp(2N) and SO(2N). Consequently, we show that in each of these Brownian motion models, as one varies the system size L, a third order phase transition occurs at a critical value L=L_c(N)\sim \sqrt{N} in the large N limit. Close to the critical point, the reunion probability, properly centered and scaled, is identical to the Tracy-Widom distribution describing the probability distribution of the largest eigenvalue of a random matrix. For the periodic case we obtain the Tracy-Widom distribution corresponding to the GUE random matrices, while for the absorbing and reflecting cases we get the Tracy-Widom distribution corresponding to GOE random matrices. In the absorbing case, the reunion probability is also identified as the maximal height of N non-intersecting Brownian excursions ("watermelons" with a wall) whose distribution in the asymptotic scaling limit is then described by GOE Tracy-Widom law. In addition, large deviation formulas for the maximum height are also computed.Comment: 37 pages, 4 figures, revised and published version. A typo has been corrected in Eq. (10

Users' Experiences of a Mobile Health Self-Management Approach for the Treatment of Cystic Fibrosis: Mixed Methods Study

[EN] Background: Despite a large number of clinical trials aiming at evaluating the digital self-management of chronic diseases, there is little discussion about users¿ experiences with digital approaches. However, a good user experience is a critical factor for technology adoption. Understanding users¿ experiences can inform the design of approaches toward increased motivation for digital self-management. Objective: This study aimed to evaluate the self-management of cystic fibrosis (CF) with a focus on gastrointestinal concerns and the care of young patients. Following a user-centered design approach, we developed a self-management app for patients and parents and a web tool for health care professionals (HCPs). To evaluate the proposed solutions, a 6-month clinical trial was conducted in 6 European CF competence centers. This paper analyzes the user acceptance of the technology and the benefits and disadvantages perceived by the trial participants. Methods: A mixed methods approach was applied. Data were collected through 41 semistructured qualitative interviews of patients, parents, and HCPs involved in the clinical trial. In addition, data were collected through questionnaires embedded in the self-management app. Results: Support for enzyme dose calculation and nutrition management was found to be particularly useful. Patients and parents rapidly strengthened their knowledge about the treatment and increased their self-efficacy. Reported benefits include reduced occurrence of symptoms and enhanced quality of life. Patients and parents had different skills, requiring follow-up by HCPs in an introductory phase. HCPs valued obtaining precise information about the patients, allowing for more personalized advice. However, the tight follow-up of several patients led to an increased workload. Over time, as patient self-efficacy increased, patient motivation for using the app decreased and the quality of the reported data was reduced. Conclusions: Self-management enfolds a collaboration between patients and HCPs. To be successful, a self-management approach should be accepted by both parties. Through understanding behaviors and experiences, this study defines recommendations for a complex case¿the demanding treatment of CF. We identify target patient groups and situations for which the app is most beneficial and suggest focusing on these rather than motivating for regular app usage over a long time. We also advise the personalized supervision of patients during the introduction of the approach. Finally, we propose to develop guidance for HCPs to facilitate changes in practice. As personalization and technology literacy are factors found to influence the acceptance of digital self-management of other chronic diseases, it is relevant to consider the proposed recommendations beyond the case of CF.The authors of this paper, on behalf of the MyCyFAPP consortium, acknowledge the European Union and the Horizon 2020 Research and Innovation Framework Programme for funding the project (ref. 643806). The authors would like to thank all project partners for their collaboration during participant recruitment and project management. Without the dedication of participants in terms of time, effort, and valuable input, this publication would not have been possible. The authors would like to thank all the participants who contributed to this work.Floch, J.; Vilarinho, T.; Zettl, A.; Ibáñez Sánchez, G.; Calvo-Lerma, J.; Stav, E.; Halland Haro, P.... (2020). Users' Experiences of a Mobile Health Self-Management Approach for the Treatment of Cystic Fibrosis: Mixed Methods Study. JMIR mHealth and uHealth. 8(7):1-19. https://doi.org/10.2196/15896S11987Webb, T. L., Joseph, J., Yardley, L., & Michie, S. (2010). Using the Internet to Promote Health Behavior Change: A Systematic Review and Meta-analysis of the Impact of Theoretical Basis, Use of Behavior Change Techniques, and Mode of Delivery on Efficacy. Journal of Medical Internet Research, 12(1), e4. doi:10.2196/jmir.1376Free, C., Phillips, G., Galli, L., Watson, L., Felix, L., Edwards, P., … Haines, A. (2013). The Effectiveness of Mobile-Health Technology-Based Health Behaviour Change or Disease Management Interventions for Health Care Consumers: A Systematic Review. PLoS Medicine, 10(1), e1001362. doi:10.1371/journal.pmed.1001362Marcolino, M. S., Oliveira, J. A. Q., D’Agostino, M., Ribeiro, A. L., Alkmim, M. B. M., & Novillo-Ortiz, D. (2018). The Impact of mHealth Interventions: Systematic Review of Systematic Reviews. JMIR mHealth and uHealth, 6(1), e23. doi:10.2196/mhealth.8873Venkatesh, Morris, Davis, & Davis. (2003). User Acceptance of Information Technology: Toward a Unified View. MIS Quarterly, 27(3), 425. doi:10.2307/30036540Cystic Fibrosis Europe2020-05-27https://www.cf-europe.eu/Conway, S., Balfour-Lynn, I. M., De Rijcke, K., Drevinek, P., Foweraker, J., Havermans, T., … Peckham, D. (2014). European Cystic Fibrosis Society Standards of Care: Framework for the Cystic Fibrosis Centre. Journal of Cystic Fibrosis, 13, S3-S22. doi:10.1016/j.jcf.2014.03.009Floch, J., Zettl, A., Fricke, L., Weisser, T., Grut, L., Vilarinho, T., … Schauber, C. (2018). User Needs in the Development of a Health App Ecosystem for Self-Management of Cystic Fibrosis: User-Centered Development Approach. JMIR mHealth and uHealth, 6(5), e113. doi:10.2196/mhealth.8236Calvo-Lerma, J., Martinez-Jimenez, C. P., Lázaro-Ramos, J.-P., Andrés, A., Crespo-Escobar, P., Stav, E., … Ribes-Koninckx, C. (2017). Innovative approach for self-management and social welfare of children with cystic fibrosis in Europe: development, validation and implementation of an mHealth tool (MyCyFAPP). BMJ Open, 7(3), e014931. doi:10.1136/bmjopen-2016-014931Borowitz, D., Gelfond, D., Maguiness, K., Heubi, J. E., & Ramsey, B. (2013). Maximal daily dose of pancreatic enzyme replacement therapy in infants with cystic fibrosis: A reconsideration. Journal of Cystic Fibrosis, 12(6), 784-785. doi:10.1016/j.jcf.2013.05.011Calvo-Lerma, J., Fornés-Ferrer, V., Peinado, I., Heredia, A., Ribes-Koninckx, C., & Andrés, A. (2019). A first approach for an evidence-based in vitro digestion method to adjust pancreatic enzyme replacement therapy in cystic fibrosis. PLOS ONE, 14(2), e0212459. doi:10.1371/journal.pone.0212459Calvo-Lerma, J., Hulst, J., Boon, M., Martins, T., Ruperto, M., Colombo, C., … Ribes-Koninckx, C. (2019). The Relative Contribution of Food Groups to Macronutrient Intake in Children with Cystic Fibrosis: A European Multicenter Assessment. Journal of the Academy of Nutrition and Dietetics, 119(8), 1305-1319. doi:10.1016/j.jand.2019.01.003Turck, D., Braegger, C. P., Colombo, C., Declercq, D., Morton, A., Pancheva, R., … Wilschanski, M. (2016). ESPEN-ESPGHAN-ECFS guidelines on nutrition care for infants, children, and adults with cystic fibrosis. Clinical Nutrition, 35(3), 557-577. doi:10.1016/j.clnu.2016.03.004Vo, V., Auroy, L., & Sarradon-Eck, A. (2019). Patients’ Perceptions of mHealth Apps: Meta-Ethnographic Review of Qualitative Studies. JMIR mHealth and uHealth, 7(7), e13817. doi:10.2196/13817Anderson, K., Burford, O., & Emmerton, L. (2016). Mobile Health Apps to Facilitate Self-Care: A Qualitative Study of User Experiences. PLOS ONE, 11(5), e0156164. doi:10.1371/journal.pone.0156164Boon, M., Calvo-Lerma, J., Claes, I., Havermans, T., Asseiceira, I., Bulfamante, A., … Ribes-Koninckx, C. (2020). Use of a mobile application for self-management of pancreatic enzyme replacement therapy is associated with improved gastro-intestinal related quality of life in children with Cystic Fibrosis. Journal of Cystic Fibrosis, 19(4), 562-568. doi:10.1016/j.jcf.2020.04.001Hevner, March, Park, & Ram. (2004). Design Science in Information Systems Research. MIS Quarterly, 28(1), 75. doi:10.2307/25148625-ISO 9241-210:2010 Ergonomics of Human-System Interaction — Part 210: Human-Centred Design for Interactive SystemsInternational Organization for Standardization20102020-06-05https://www.iso.org/standard/52075.htmlVilarinho, T., Floch, J., & Stav, E. (2017). Co-designing a mHealth Application for Self-management of Cystic Fibrosis. Lecture Notes in Computer Science, 3-22. doi:10.1007/978-3-319-67687-6_1Kristensen, G. K., & Ravn, M. N. (2015). The voices heard and the voices silenced: recruitment processes in qualitative interview studies. Qualitative Research, 15(6), 722-737. doi:10.1177/1468794114567496Etikan, I. (2016). Comparison of Convenience Sampling and Purposive Sampling. American Journal of Theoretical and Applied Statistics, 5(1), 1. doi:10.11648/j.ajtas.20160501.11Bryman, A. (2006). Integrating quantitative and qualitative research: how is it done? Qualitative Research, 6(1), 97-113. doi:10.1177/1468794106058877Klein, H. K., & Myers, M. D. (1999). A Set of Principles for Conducting and Evaluating Interpretive Field Studies in Information Systems. MIS Quarterly, 23(1), 67. doi:10.2307/249410Braun, V., & Clarke, V. (2006). Using thematic analysis in psychology. Qualitative Research in Psychology, 3(2), 77-101. doi:10.1191/1478088706qp063oaLee, Y., Kozar, K. A., & Larsen, K. R. T. (2003). The Technology Acceptance Model: Past, Present, and Future. Communications of the Association for Information Systems, 12. doi:10.17705/1cais.01250Calvo-Lerma, J., Hulst, J. M., Asseiceira, I., Claes, I., Garriga, M., Colombo, C., … Ribes-Koninckx, C. (2017). Nutritional status, nutrient intake and use of enzyme supplements in paediatric patients with Cystic Fibrosis; a European multicentre study with reference to current guidelines. Journal of Cystic Fibrosis, 16(4), 510-518. doi:10.1016/j.jcf.2017.03.005Johnson, K. B., Patterson, B. L., Ho, Y.-X., Chen, Q., Nian, H., Davison, C. L., … Mulvaney, S. A. (2015). The feasibility of text reminders to improve medication adherence in adolescents with asthma. Journal of the American Medical Informatics Association, 23(3), 449-455. doi:10.1093/jamia/ocv158Granger, D., Vandelanotte, C., Duncan, M. J., Alley, S., Schoeppe, S., Short, C., & Rebar, A. (2016). Is preference for mHealth intervention delivery platform associated with delivery platform familiarity? BMC Public Health, 16(1). doi:10.1186/s12889-016-3316-2Cook, K. A., Modena, B. D., & Simon, R. A. (2016). Improvement in Asthma Control Using a Minimally Burdensome and Proactive Smartphone Application. The Journal of Allergy and Clinical Immunology: In Practice, 4(4), 730-737.e1. doi:10.1016/j.jaip.2016.03.005Cafazzo, J. A., Casselman, M., Hamming, N., Katzman, D. K., & Palmert, M. R. (2012). Design of an mHealth App for the Self-management of Adolescent Type 1 Diabetes: A Pilot Study. Journal of Medical Internet Research, 14(3), e70. doi:10.2196/jmir.2058Riis, A., Hjelmager, D. M., Vinther, L. D., Rathleff, M. S., Hartvigsen, J., & Jensen, M. B. (2018). Preferences for Web-Based Information Material for Low Back Pain: Qualitative Interview Study on People Consulting a General Practitioner. JMIR Rehabilitation and Assistive Technologies, 5(1), e7. doi:10.2196/rehab.8841Goetz, M., Müller, M., Matthies, L. M., Hansen, J., Doster, A., Szabo, A., … Wallwiener, S. (2017). Perceptions of Patient Engagement Applications During Pregnancy: A Qualitative Assessment of the Patient’s Perspective. JMIR mHealth and uHealth, 5(5), e73. doi:10.2196/mhealth.7040Giunti, G., Kool, J., Rivera Romero, O., & Dorronzoro Zubiete, E. (2018). Exploring the Specific Needs of Persons with Multiple Sclerosis for mHealth Solutions for Physical Activity: Mixed-Methods Study. JMIR mHealth and uHealth, 6(2), e37. doi:10.2196/mhealth.8996Aujoulat, I., d’ Hoore, W., & Deccache, A. (2007). Patient empowerment in theory and practice: Polysemy or cacophony? Patient Education and Counseling, 66(1), 13-20. doi:10.1016/j.pec.2006.09.008Waite-Jones, J. M., Majeed-Ariss, R., Smith, J., Stones, S. R., Van Rooyen, V., & Swallow, V. (2018). Young People’s, Parents’, and Professionals’ Views on Required Components of Mobile Apps to Support Self-Management of Juvenile Arthritis: Qualitative Study. JMIR mHealth and uHealth, 6(1), e25. doi:10.2196/mhealth.9179Lubberding, S., van Uden-Kraan, C. F., Te Velde, E. A., Cuijpers, P., Leemans, C. R., & Verdonck-de Leeuw, I. M. (2015). Improving access to supportive cancer care through an eHealth application: a qualitative needs assessment among cancer survivors. Journal of Clinical Nursing, 24(9-10), 1367-1379. doi:10.1111/jocn.12753Simons, L., Valentine, A. Z., Falconer, C. J., Groom, M., Daley, D., Craven, M. P., … Hollis, C. (2016). Developing mHealth Remote Monitoring Technology for Attention Deficit Hyperactivity Disorder: A Qualitative Study Eliciting User Priorities and Needs. JMIR mHealth and uHealth, 4(1), e31. doi:10.2196/mhealth.5009Velu, A. V., van Beukering, M. D., Schaafsma, F. G., Frings-Dresen, M. H., Mol, B. W., van der Post, J. A., & Kok, M. (2017). Barriers and Facilitators for the Use of a Medical Mobile App to Prevent Work-Related Risks in Pregnancy: A Qualitative Analysis. JMIR Research Protocols, 6(8), e163. doi:10.2196/resprot.7224Switsers, L., Dauwe, A., Vanhoudt, A., Van Dyck, H., Lombaerts, K., & Oldenburg, J. (2018). Users’ Perspectives on mHealth Self-Management of Bipolar Disorder: Qualitative Focus Group Study. JMIR mHealth and uHealth, 6(5), e108. doi:10.2196/mhealth.9529Al Dahdah, M. (2017). Health at her fingertips: development, gender and empowering mobile technologies. Gender, Technology and Development, 21(1-2), 135-151. doi:10.1080/09718524.2017.1385701Consolvo, S. (2012). Designing for Healthy Lifestyles: Design Considerations for Mobile Technologies to Encourage Consumer Health and Wellness. Foundations and Trends® in Human–Computer Interaction, 6(3–4), 167-315. doi:10.1561/110000004

Jet quenching in hot strongly coupled gauge theories simplified

Theoretical studies of jet stopping in strongly-coupled QCD-like plasmas have used gauge-gravity duality to find that the maximum stopping distance scales like E^{1/3} for large jet energies E. In recent work studying jets that are created by finite-size sources in the gauge theory, we found an additional scale: the typical (as opposed to maximum) jet stopping distance scales like (EL)^{1/4}, where L is the size of the space-time region where the jet is created. In this paper, we show that the results of our previous, somewhat involved computation in the gravity dual, and the (EL)^{1/4} scale in particular, can be very easily reproduced and understood in terms of the distance that high-energy particles travel in AdS_5-Schwarzschild space before falling into the black brane. We also investigate how stopping distances depend on the conformal dimension of the source operator used to create the jet.Comment: 30 pages, 10 figure

Barriers to and Facilitators of Engagement With mHealth Technology for Remote Measurement and Management of Depression: Qualitative Analysis

BACKGROUND: Mobile technology has the potential to provide accurate, impactful data on the symptoms of depression, which could improve health management or assist in early detection of relapse. However, for this potential to be achieved, it is essential that patients engage with the technology. Although many barriers to and facilitators of the use of this technology are common across therapeutic areas and technology types, many may be specific to cultural and health contexts. OBJECTIVE: This study aimed to determine the potential barriers to and facilitators of engagement with mobile health (mHealth) technology for remote measurement and management of depression across three Western European countries. METHODS: Participants (N=25; 4:1 ratio of women to men; age range, 25-73 years) who experienced depression participated in five focus groups held in three countries (two in the United Kingdom, two in Spain, and one in Italy). The focus groups investigated the potential barriers to and facilitators of the use of mHealth technology. A systematic thematic analysis was used to extract themes and subthemes. RESULTS: Facilitators and barriers were categorized as health-related factors, user-related factors, and technology-related factors. A total of 58 subthemes of specific barriers and facilitators or moderators emerged. A core group of themes including motivation, potential impact on mood and anxiety, aspects of inconvenience, and ease of use was noted across all countries. CONCLUSIONS: Similarities in the barriers to and facilitators of the use of mHealth technology have been observed across Spain, Italy, and the United Kingdom. These themes provide guidance on ways to promote the design of feasible and acceptable cross-cultural mHealth tools. ©Sara Simblett, Faith Matcham, Sara Siddi, Viola Bulgari, Chiara Barattieri di San Pietro, Jorge Hortas López, José Ferrão, Ashley Polhemus, Josep Maria Haro, Giovanni de Girolamo, Peter Gamble, Hans Eriksson, Matthew Hotopf, Til Wykes, RADAR-CNS Consortium. Originally published in JMIR Mhealth and Uhealth (http://mhealth.jmir.org), 30.01.2019

Extreme damped Lyman-α\alpha absorption in young star-forming galaxies at z=9−11z=9-11

The onset of galaxy formation is thought to be initiated by the infall of neutral, pristine gas onto the first protogalactic halos. However, direct constraints on the abundance of neutral atomic hydrogen (HI) in galaxies have been difficult to obtain at early cosmic times. Here we present spectroscopic observations with JWST of three galaxies at redshifts $z=8.8 - 11.4$, about $400-600$ Myr after the Big Bang, that show strong damped Lyman-$\alpha$ absorption ($N_{\rm HI} > 10^{22}$ cm$^{-2}$) from HI in their local surroundings, an order of magnitude in excess of the Lyman-$\alpha$ absorption caused by the neutral intergalactic medium at these redshifts. Consequently, these early galaxies cannot be contributing significantly to reionization, at least at their current evolutionary stages. Simulations of galaxy formation show that such massive gas reservoirs surrounding young galaxies so early in the history of the universe is a signature of galaxy formation in progress.Comment: Submitte

The Association Between Home Stay and Symptom Severity in Major Depressive Disorder: Preliminary Findings From a Multicenter Observational Study Using Geolocation Data From Smartphones

BACKGROUND: Most smartphones and wearables are currently equipped with location sensing (using GPS and mobile network information), which enables continuous location tracking of their users. Several studies have reported that various mobility metrics, as well as home stay, that is, the amount of time an individual spends at home in a day, are associated with symptom severity in people with major depressive disorder (MDD). Owing to the use of small and homogeneous cohorts of participants, it is uncertain whether the findings reported in those studies generalize to a broader population of individuals with MDD symptoms. OBJECTIVE: The objective of this study is to examine the relationship between the overall severity of depressive symptoms, as assessed by the 8-item Patient Health Questionnaire, and median daily home stay over the 2 weeks preceding the completion of a questionnaire in individuals with MDD. METHODS: We used questionnaire and geolocation data of 164 participants with MDD collected in the observational Remote Assessment of Disease and Relapse-Major Depressive Disorder study. The participants were recruited from three study sites: King's College London in the United Kingdom (109/164, 66.5%); Vrije Universiteit Medisch Centrum in Amsterdam, the Netherlands (17/164, 10.4%); and Centro de Investigación Biomédica en Red in Barcelona, Spain (38/164, 23.2%). We used a linear regression model and a resampling technique (n=100 draws) to investigate the relationship between home stay and the overall severity of MDD symptoms. Participant age at enrollment, gender, occupational status, and geolocation data quality metrics were included in the model as additional explanatory variables. The 95% 2-sided CIs were used to evaluate the significance of model variables. RESULTS: Participant age and severity of MDD symptoms were found to be significantly related to home stay, with older (95% CI 0.161-0.325) and more severely affected individuals (95% CI 0.015-0.184) spending more time at home. The association between home stay and symptoms severity appeared to be stronger on weekdays (95% CI 0.023-0.178, median 0.098; home stay: 25th-75th percentiles 17.8-22.8, median 20.9 hours a day) than on weekends (95% CI -0.079 to 0.149, median 0.052; home stay: 25th-75th percentiles 19.7-23.5, median 22.3 hours a day). Furthermore, we found a significant modulation of home stay by occupational status, with employment reducing home stay (employed participants: 25th-75th percentiles 16.1-22.1, median 19.7 hours a day; unemployed participants: 25th-75th percentiles 20.4-23.5, median 22.6 hours a day). CONCLUSIONS: Our findings suggest that home stay is associated with symptom severity in MDD and demonstrate the importance of accounting for confounding factors in future studies. In addition, they illustrate that passive sensing of individuals with depression is feasible and could provide clinically relevant information to monitor the course of illness in patients with MDD