JavaScript is disabled. Please enable Javascript for full website functionality. To learn how to enable Javascript visit

The Connector - Fall 2020 Issue

Visualizing Evidence: How Systems Dynamicists At the Sax Institute Are Helping Decisionmakers Find Insights in Data

Danielle Currie Danielle Currie

Australia is a country of swimmers. Every child learns to swim and frequents school and municipal pools throughout their lives. Unfortunately, while Australians are getting great exercise, they sometimes come in contact with cryptosporidium, a fecal parasite spread by infected swimmers that is resistant to levels of chlorine used for pool water disinfection. The result of cryptosporidium infection is severe, prolonged diarrhea.

“Cryptosporidium is not particular to Australia,” says Danielle Currie, PhD, Senior Simulation Modeller at Sax Institute in Sydney, Australia. “But because swimming is such an important part of Australian culture and pools are effective transmission spots, it is a public health problem.”

The investigation of cryptosporidium transmission in public pools was Currie’s first experience in applied systems dynamics. Through a chance meeting with Carl Smith, PhD, University of Queensland, Currie learned about both system dynamics and Stella® and found a path to her own PhD dissertation and career.

“While working as an environmental officer for the Canadian government, I realized how intertwined environmental and human health are,” says Currie. “I also saw how difficult it was for decisionmakers to apply evidence to their questions. I do not have a background in math or engineering and neither do most policymakers. Looking at screens of numbers and code is mind numbing. Once I saw that nice-looking interfaces could be made using system dynamics software and used to leverage data to develop shared insights, my path was set.”

After taking a year for self-teaching in system dynamics, Currie felt ready to apply her knowledge to a real, current environmental health problem. She chose cryptosporidium infection through pools from a list of options provided by local agencies. The result was her dissertation, “Taking the ‘poo’ out of ‘pool’: Participatory systems modelling as a decision-support tool for even the messiest public environmental health problems.”

“I developed a model based on pools in the Brisbane and Gold Coast region,” says Currie. “Since Australians tend to visit multiple pools, transmission happens between facilities. I used available disease rate data as well as data for pool use, doctor visits, and dates of past infection outbreaks.”

Variables included the chance of accidental fecal release (AFR), chance of lifeguards noting and reacting to AFR, and chance of other conditions that spur infection outbreaks. “The model was able to match the documented trend in infection outbreaks which built confidence that it reflected the problem and actual conditions,” says Currie.

Prior to seeing the model and simulations of different scenarios, decisionmakers thought that cryptosporidium infections were cyclical and that current practice, e.g., shocking pools with levels of chlorine high enough to kill parasites, could solve the problem. The model, however, illustrated that the problem is random, rather than cyclical. “People had remembered infection outbreaks as every three years or so but, with the model, we could zoom out in time and see that outbreaks were random,” says Currie. “That meant we could not treat pools on an understood cycle.”

“When we began the project, our goal was outbreak prevention,” says Currie, “The insights gained through modeling and simulation completely shifted our thinking. We couldn’t prevent outbreaks, but we could manage them.” Management required understanding how the parasite was entering pools and what was happening when people became infected.

“By talking to a lot of people, we realized that international travel was playing a bigger role than expected in the transmission of cryptosporidium,” says Currie. “Parasites are picked up in other countries, brought back to Australia, and transmitted through swimming pool use. There’s no practical way to screen out international travelers who might have picked up a parasite.”

Stock and flow model of infection imported by travelers Stock and flow model of infection imported by travelers.

Currie and her project participants also realized the difference between small pools and large pools. “Smaller pools used by younger children who are learning to swim or elderly swimmers are more prone to AFR and can be shocked with high doses of chlorine that do kill the parasite when necessary,” says Currie. “While shocking is expensive and requires pool closure for a period of time, it’s not a practical solution for large pools – but there is less chance of AFR in pools used by fit adults.”

A critical mitigation action occurs outside of swimming facilities. “General medical practitioners are usually the people that hear about cases of diarrhea,” says Currie. “They might think that it’s a simple case and recommend that patients stay away from swimming pools for a few days. But cryptosporidium infection is active for two weeks. If advice to stay out of pools for that period of time is given early enough, outbreaks can be more easily contained. Educating physicians and changing the way they counsel patients was a key recommendation.”

Stock and flow diagram of complete Public Aquatic Facility Sector Stock and flow diagram of complete Public Aquatic Facility Sector.

Currie’s dissertation experience helped participating local decisionmakers understand a complex problem and discover real solutions. It earned the Lupina Young Researchers Award and an Honorable Mention in the 2019 Dana Meadows Award from the System Dynamics Society. For her ongoing work, it reinforced the importance of participatory model building and visual presentation of information and insights, two features of the Decision Analytics practice Currie joined at the Sax Institute, where work focuses on improving efficacy of health programs and services.

“Clients see the benefit of system dynamics when they participate in its application to their own project,” says Currie. “We follow a three-step process for participation that includes clients, experts, and people with experience in every step of model building, simulation running, and insight sharing.”

First, participants meet to introduce and scope out the project. “We roll out butcher paper, draw a conceptual map, and ask ‘What is the problem?’ and ‘What are the main factors?’. We also list any intervention ideas. We know that by the time a project comes to us, several interventions are already on the table and want to be sure that the model allows us to consider them.”

Currie then spends about a month or two building a draft model before the whole group meets for the second step. “Together, we work through every step of the model,” says Currie. “The model builder has to be humble and take in all feedback. I’m not a problem expert but someone who can translate expertise and feedback into modeling language and structure.” Interventions are more discretely defined so that they can be cost analyzed.

The third meeting is held after the model has been edited to include feedback and intervention details. “We work through the interface,” says Currie. “Participants actually sit in front of computers and use the model. Participants are new to system dynamics and have never used Stella but they know what’s under the hood. They’re able to use sliders, change assumptions, and look for collective aha moments.”

Currie discusses the model with stakeholders Currie discusses the model with stakeholders.

Between each step are many questions, discussions, and model reviews. “By the time we get to the end of the project, every participant has seen and commented on the model a lot,” says Currie. “With that high level of participation, we get a very balanced view of a problem. For example, when we model health concerns like cardiovascular disease or osteoporosis, we’re able to build in feedback from health agency officials, physicians, researchers, and patients to deliver insights that they all understand.”

Currie and her Sax Institute colleagues have developed over 20 models using Stella, engaging clients and participant groups in investigations of heart disease, suicide, smoking rates, alcohol consumption, gestational diabetes and other, complex, public health issues. Engagement in modeling, Currie explains, depends on having engaging models.

“Sixty percent of effective system dynamics is dependent on what’s inside the model,” says Currie. “Forty percent depends on how it looks. Using Stella’s animation feature, I’ve upped our visualization game. Models look very professional but, even more important, they’re accessible to people who are new to system dynamics. Including an animated beating heart in a cardiovascular disease model, for instance, doesn’t add important information, but it does tailor the model to participants’ interests and concerns, and encourages them to dig in.”

Stella® Helps CUNY Students Model Through the Pandemic

COVID-19 wrecked the summer of 2020 for almost everyone. Family vacations? Cancelled. Summer camp? Cancelled. Live sporting events? Cancelled. But for Liushan Wuchen and Jorin Dawidowicz, two students in the City University of New York’s Summer Undergraduate Research Program (CSURP), summer plans weren’t cancelled, just modified.

CSURP is a highly selective program that typically matches undergraduate students in summer experiential programs across the University. Some have also been placed in one of five Initiatives at the Advanced Science Research Center (ASRC)—environmental science, nanoscience, neuroscience, photonics, and structural biology—where they work with one another and mentors to contribute to research projects. "CSURP is geared toward recruiting great students," says Effie MacLachlan, PhD, Interim University Assistant Dean. "This year we selected 20 students from an applicant pool of 230. Typically, there is a lot of personal interaction. With everything shut down by COVID-19, we knew it was not the time to be bringing undergraduates into the lab. At the same time, cancelling the program would have diminished those students’ opportunities moving forward. We’re at the forefront of research. We had to learn how to pivot to a virtual program."

This pivot required two things. First, applications were screened to ensure that candidates had the experience and skills in computation, coding, and data analysis to contribute to research without daily, face-to-face instruction. Second, the program needed to employ applications and platforms that support online collaboration.

Liushan Wuchen Liushan Wuchen

Wuchen and Dawidowicz met the first criterion for the Environmental Sciences Initiative, an initiative that involves CSURP participants in ongoing research. "Liushan had some background in environmental engineering and was interested in learning more about the nitrogen cycle, and Jorin is a chemical engineering student with some understanding of energy systems," says Ehsan Najafi, PhD, Postdoctoral Research Associate, Environmental Sciences Initiative. "We met with them and offered topics that were important to the Initiative. Liushan investigated nitrogen pollution in water and Jorin researched the impact of upstream power plant thermal emissions on waterways and on downstream power stations. They are both so smart and were able to catch up with background information in just a couple of weeks before beginning to analyze systems using models."

Jorin Dawidowicz Jorin Dawidowicz

The second criterion was met, in part, by Stella. Neither Wuchen or Dawidowicz had any instruction or experience in system dynamics, let alone Stella, but both rapidly developed the necessary skills over the course of eight weeks before presenting their final work. "System dynamics was all new to me," says Dawidowicz. "I used a YouTube tutorial to learn Stella’s basic functions and saw that it was very visual and intuitive."

The students worked on their own during the week and connected with Najafi and Charles J. Vörösmarty, PhD—the Director of the ASRC Environmental Sciences Initiative—on Fridays to review progress, ask questions, and get advice. "I revised my model every week," says Wuchen. "I wanted to use array functions and was able to get help from another person in the program who had Stella experience."

While Vörösmarty has decades of systems dynamics experience, he could relate to the challenge presented to his students. "Almost 40 years ago, I took a course in Systems Ecology from professor Charles Hall while at Cornell University," says Vörösmarty. "Looking at systems operating as a whole was very new and we were thrown into the deep end of the pool. We learned about systems in general and how to analyze them using computers, which meant we also had to learn how to code. At the time, that required decks of punched cards fed into mainframe computers. I also learned the importance of having a good mentor. It was a life-changing experience."

Prior to CUNY, Vörösmarty was on the faculty of the University of New Hampshire. There he pioneered the field of global hydrology and water resource assessment based on complex geospatial models that required computers, and weeks or months to set up and run. The Initiative continues to use those large models but Vörösmarty, with the help of Najafi, is working to create simplified models that can be used on their own or connected as needed, particularly useful in the work they are pursuing with non-technical communities.

"We want to reduce run times and make the models and output more accessible to stakeholders," says Najafi. "By modelling power plant thermal pollution and point and non-point source pollution that leads to algae growth and impacts fish populations, for example, we can engage stakeholders in the co-design of better scenarios." As a result of this summer’s CSURP program, two simplified models created by Luishan and Dawidowicz are ready for use and further development in this context.

Wuchen’s model, a nitrogen source and transport simulation using Stella, simulates the impact of sewage and fertilizer runoff on instream pollution levels. It monitors nitrogen transportation from atmospheric, organic, and inorganic sources to the land (soil and groundwaters) and from the land to lakes, reservoirs, and rivers before entering the ocean. It includes links to watershed and thermal pollution models to simulate fuller, more complex scenarios.

Wuchen's nitrogen transportation model Wuchen's nitrogen transportation model.

"The model is a good way to show policy makers how an increase in population or cropland expansion leads to an increase in nitrogen transfer to water," says Wuchen. "We still need to add some features to the model and to input new data so that we can understand the nitrogen cycle’s relationship to climate, food, energy, and water security."

Dawidowicz modeled thermal power plant emissions. Both fossil and nuclear fuel power plants transfer between 60% and 70% of the energy they generate into the environment as heat, particularly when they use once-through cooling from surface water supplies. Increased water temperatures encourage algae growth, starve fish populations of oxygen, and reduce the efficiency of downstream plants that require cool water for efficient operation.

Part of Dawidowicz's thermal power emissions model Part of Dawidowicz's thermal power emissions model.

"The model simulates the flow of energy from a thermoelectric power plant and the impact of its operations on downstream plants and the river itself," says Dawidowicz. "I developed the model by stripping down an existing model called Thermoelectric Power and Thermoelectric Pollution Model that was created by Professor Vörösmarty and his colleagues."

The current version of Dawidowicz’s model treats the movement of water past a series of four hypothetical power plants—a coal-fired plant, a nuclear plant, and two additional coal plants. The first three transport waste heat by running water from the river through the plant, and then release it back into the river. The fourth uses a cooling tower that releases heat into the air, with much less impact on the adjacent river.

The model demonstrates that river water temperature sequentially increases as it passes through each power plant, reducing each successive plant’s efficiency. Dawidowicz analyzes the power and thermal pollution generated by each plant. The first plant has the capacity to produce a peak of 500 MW of electricity. The next two plants attempt to reach that level, but are handicapped by higher intake temperatures, which reduces their efficiencies.

"The model is a work in progress," says Dawidowicz. "It could be developed further by adding more power plant technologies, testing it with real-world data, and linking it to other Stella models like a watershed or agricultural water use model."

"While working with these students, we’ve learned that we can help them get into the guts of a system to make a pretty thorough but simple model," says Vörösmarty. "Now Ehsan and I need to make sure that the simple models don’t get too complex. That can be a challenge given the tendency to keep adding to models past the point where they can be used to answer practical questions for stakeholders with reasonable set-up and run times.

"We really want to keep working with Liushan and Jorin. We are thrilled that Liushan is taking a new Senior Design project class that combines earth science and environmental engineering. She’s recruited four other students to join her. Jorin will continue his work through an honors project."

"The pandemic taught us that it’s possible for students to learn and collaborate remotely," says Najafi. "They were able to learn Stella quickly and we were able to rapidly evaluate their progress and offer advice and encouragement. That said, it would be really nice to meet Liushan and Jorin in person!"

Looking Forward to the Spring Semester

We want to congratulate universities, colleges and schools for continuing to adapt to the pandemic. As the spring semester draws near, we also want to remind you of the policies we have in place to aid remote learning.

  • Lab packs may be used on cloud-based services such as Citrix and AWS app stream or through remote desktops with a license server. If you have not already put a license server in place, you would need to do so to assure only the number of licenses owned are used concurrently.


  • If lab packs have active support contracts, customers can be set up with licenses to Stella® Professional Online for the entire semester.
  • If lab packs have active support contracts, we can convert them to student pack licenses. Student pack licenses can be issued out to students for a given length of time and can be installed on their personal computers. After the expiration date has been reached, the licenses can be reissued to new students.

Please contact customer service if you have any questions or concerns on getting access for your students or faculty.

Stella Users Network

If you have not yet, join our Stella Users Network group. Here you can receive answers and comments directly from us, as well as from a community of experienced modelers. Many modelers are already members, and the more members, the better it will be. We have been overjoyed with the feedback questions and posts have received. To join, go here and click on Join This Group at the bottom. Should you have questions or issues about signing up, please email us.

Software Update

Version 2.0.2 is now available. To learn more about the new features, visit our feature updates page.

On the Road…Sort Of

We have been doing a lot of travel lately…virtually, that is. In late October, Co-president Karim Chichakly attended the 18th annual Latin American Conference on System Dynamics hosted by Universidad Autónoma de Bucaramanga, Colombia. This virtual conference held an impressive 25 plenaries and 90 parallel sessions presented from all over the world. Karim presented his work "Modeling Covid-19 Polices," which can now be viewed online. Currently, Karim is attending the 8th South African System Dynamics Conference hosted by Eskom Research Testing & Development, Johannesburg, South Africa. Karim will be presenting the keynote on Systems Thinking for Public Policy: A Case Study in Brazil. The 3rd annual System Dynamic Competition included an impressive 28 competitors and the challenge this year was for competitors to identify an area of interest around them and how it has been affected by COVID-19. isee systems was happy to sponsor the software for the competitors and facilitators for this competition. We would like to congratulate the winner Yong Sebastian Nyam, for his work on the effect of COVID-19 on the blooming citrus farming industry in South Africa.

Finally, isee systems would like to congratulate our lead developer, Billy Schoenberg, for completing and successfully defending his PhD on November 6th at the University of Bergen, Norway. Billy has been working and traveling for over three years to complete his PhD on Loops That Matter, and his hard work was implemented in Stella 2.0. Due to the pandemic, his defense was held virtually, allowing many to attend.

Upcoming Events

Recent Posts

Spring 2020 Issue

A social scientist uses system dynamics to improve early childhood education, a professor uses Stella to model the relationship between economy and environment, lead developer Billy Schoenberg shares the history of Stella's new Loops That Matter™ feature, the new Beer Game, isee systems' response to COVID-19, and isee systems goes (virtually) on the road...

Fall 2019 Issue

A PhD student designs a plan to save water with Stella®, a credit union CEO collaborates with a system dynamics expert to better help his customers, Jon Darkow shares Stella tips and tricks, the 2020 isee user conference, new online courses, the next Barry Richmond Award, and isee systems heads to Australia...

Spring 2019 Issue

A former international development consultant uses Systems Thinking to analyze border security, a simulations expert tackles healthcare with Stella® Architect, Stella® Professional Online™ becomes the newest isee systems product, partners share their latest achievements, students present their modeling projects, new training and resources, and isee systems heads to Albuquerque...

Phone: (603) 448-4990 Email:

   Monday - Friday: 9:00 am - 5:00 pm EDT | Saturday - Sunday: Closed
24 Hanover St, Ste 8A | Lebanon, NH 03766 | US

isee systems inc. holds trademarks registered in the U.S. Patent and Trademark Office for iThink®, Stella®, isee systems® and claims the following trademarks; isee NetSim™, isee Exchange™, Stella Live™, Causal Lens™, Stella Online™, Stella Professional Online™, and Assemblies™.

Terms of Use

© 2024. isee systems inc . All rights reserved.