Engaging Science Students with STELLA
The complex, elegant systems and cycles that make up the human body and the natural world are fascinating.
Using lectures, blackboard diagrams, or even animations to explain those systems and cycles can make them
incomprehensible and, well, boring. That’s why Jon Darkow uses Stella, Systems Thinking software from
isee systems, to teach biology, anatomy and physiology, and environmental science to students at Seneca
High School in rural, northwest Ohio.
“I started using modeling software in graduate school at Bowling Green University,” says Darkow. “It was
an organic learning process – I was self-taught – and I tried to integrate a couple of applications into
my high school classes. Through the Creative Learning Exchange, I heard that Stella was easier to use and
discovered that the last protocol in a curriculum called Watershed Dynamics used a Stella model to make
decisions on water use. I thought, ‘I have to get this software.’”
Darkow wrote a grant and secured a district-wide site license. That was four years ago. Since then he’s
developed models that allow students to learn about physiological, biological, ecological and environmental
systems through experimentation and discovery.
One of Darkow’s models simulates the cellular respiration process. “Cellular respiration is very complicated,
very dynamic and there are lots of interactions,” says Darkow. “We use the model to answer the question
‘How do you get energy from a glucose molecule to make adenosine triphosphate, ATP?’ The model makes it
easier for students to see how the process works over time.”
Students don’t just passively watch the model. They manipulate four sliders to test the influence of oxygen,
temperature, pH, and other chemical variables on ATP production at every phase of the cycle. “When students
play with the model they see that the cycle works better with a lower pH level, for example,” says Darkow.
There are several indications that Darkow’s cellular respiration model is an effective teaching tool.
“At the beginning of the year, I chose the data table they would use for variable analysis,” says Darkow.
“I’d prescribe the X-axis and the Y-axis. By the end of the year students had become better thinkers.
They could make their own data tables and graphs and choose their own variables. And when tested on
cellular respiration, they did better than students who had been taught through animations.”
Cell respiration model
Inspired by the Ohio Teacher Showcase that highlights the work of teachers engaged in project-based education,
Darkow created a template for a natural selection model. “I got the idea from Barry Richmond’s book,” says
Darkow. “My students have to adapt the model to their own study of natural selection. One student looked
at the evolution of lactose-persistency in herding communities. Another is looking at sickle cell anemia
in areas with malaria.”
Before modeling natural selection, students spend a lot of time choosing the variables they’ll test.
“The model forces them to think about how variables will increase or decrease in certain conditions,”
says Darkow. “Students have to engage in trial and error. They see a screwy thing happen, develop a
hypothesis, test the hypothesis, make revisions, and test again.”
This spring, the top six natural selection models from Darkow’s class were presented to professors from
Heidelberg College. “I’ve been really impressed with their work. By researching an HIV-resistant gene in places
where there is a high rate of HIV infection, one group even managed to find the intersection of biology,
ecology, and social dynamics.”
Darkow does teach some AP-level classes but he’s quick to point out that he’s not always putting Stella in
the hands of academic high-fliers. “I teach regular rural kids,” he says. “I had one student who wasn’t
that into class – he doodled a lot,” says Darkow. “But he just took charge with his model and even went
around to help other groups. He’s like me, not that interested in details, but loves testing things over
and over to see what changed. With Stella, he just blossomed.”
His and his students’ appreciation for variable testing have made Stella’s sliders and graphs two of Darkow’s
favorite features. “Sliders and comparative graphs allows students to discover small manipulations that make
big changes,” says Darkow. Other features have made it easier for Darkow to model specific systems. “The Random
feature is very useful in AP biology classes where students have to understand natural variation. I was having
trouble getting genetic drift and natural selection ideas into models and the built-in binomial function helped
me figure that out.”
Stella’s ability to handle large amounts of data also adds to its capacity as an educational tool. “Stella puts
computing back in the computer,” says Darkow. “Crunching numbers is something computers are really good at.
I was able to teach about population growth by running a million generations during a one-period class. I
couldn’t do that without Stella and a computer.”
NetSim has made it easy for Darkow’s students to play with models outside of class and for him to share his
work with thousands of peers. “My enzyme simulation has been run over 4,000 times,” says Darkow. “I link to
it from the College Board AP Biology site. The feedback has been very positive, everything from ‘This is great’
to detailed questions from teachers who want to be sure they’re on the right track.”
As happy as he is to share his models with other teachers, Darkow hopes that more and more teachers start
using Stella on their own. “There is a definite learning curve but the more you use Stella, the more confident
you become,” says Darkow. “I’m doing more this year than ever before and I’m more comfortable making models
that are realistic.”
“The best way to learn about modeling is to start with something simple and then experiment with more and
more complexity,” says Darkow. “The more you play, the more interesting and fun it gets. It’s like a game.”
And, just like science, Darkow finds that modeling is best learned through trial and error.
He’s experimenting with more complexity himself. “I’m thinking about where I’m headed next with teaching
about environmental problems and looking at leverage points,” says Darkow. “I just love the creativity
Stella allows. As an educational tool, it’s awesome.”
iThink dynamic modeling improves freight and passenger transportation systems on Latin America’s borders
For developing countries, building international trade capabilities is often the key to economic success.
Trade opens new markets and allows small producers to grow. It invites tourism and job opportunities for
migrants and immigrants who will contribute their earnings to local economies. Implementing systems that
control efficient trade is often the challenge that gets between trade aspirations and actual economic gains.
“Since 1959, the Transport Division of the Inter-American Development Bank (IADB) has worked to improve the fluidity
and control of freight and passenger processes at borders,” says Graciela Sicra, Principal of OMN Systemic Strategy,
an isee systems consulting and training partner. “Through several projects, it developed the concept of Integrated
Control Centers (ICC). Specializing in freight and passenger systems, each ICC functions as a binational city;
within its boundaries, there is free movement of people and goods.”
ICCs aim to improve the operational efficiency of border crossings and ensure the integrity of control processes
for both freight and people. To increase efficiency, ICCs have to decrease the unplanned down time that is often
the result of private agent staffing practices or unanticipated flows of people and freight. Decreasing downtime
depends on a thorough understanding of people and freight transit flows and the ability to continually optimize
To get a deeper understanding of the flows moving in and out of their transit systems and the relationship of those
flows to staffing levels, ICC project experts turned to iThink models developed by OMN Systemic Strategy. “Using the
iThink models, analysts interact with complex systems and explore, design, and test management policies and processes,”
says Sicra. Working with ICC analysts, OMN developed iThink management flight simulators for all ICC projects in
Latin America at Southern Cone country borders, as well as borders with Peru, Ecuador, Columbia, Panama, and Costa Rica.
Each project uses two models, one for passengers and one for freight, that support both the initial planning and design
of each center and its operations after construction. At the planning and design stage, the simulator provides a solid
base for sizing parking facilities, passenger and freight lines, and control posts using actual field data and projections
that look out 20 years. After the ICC has opened, the simulator provides a consistent, shared method for analysts and
decision makers to determine if operational targets will be achieved and to test additional actions that will be required.
Each simulator captures the processes observed at existing sites, thus allowing scenario analyses that compress time
and space in a framework that emphasizes:
- Transparency: The structure of the model is available and the results are displayed numerically and graphically.
- Flexibility: Models support a wide variety of complex scenarios. The data can be exported to an Excel spreadsheet.
- Consistency: The behavior of the model is consistent with observed data from existing sites.
- Accessibility: The users interact through a user-friendly interface on laptops in real time.
- Robustness: The models capture the operational details specific to each user category and vehicle.
By capturing key elements of the ICC operation, the simulator allows rapid experimentation with facility-routing
proposals and the future operation of the complex. “ICCs impose many changes at border crossings,” says Sicra.
“By using models, ICC analysts are able to demonstrate how the concept works and its benefits to the countries
and cities involved.”
Simulator User Interface
The custom-designed simulator user interface makes it possible for analysts who have no training or experience in
systems dynamics or modeling to interact with passenger and freight control processes. The impact of their decisions
are displayed using indicators, tables, and charts. By changing the operational parameters, analysts can verify the
validity of their proposals under a variety of scenarios.
For example, analysts optimize the passenger control process by modeling flows of people in each direction through
the ICC’s control facilities, looking at both mode of transportation (foot, car, or bus) and classification of person
(tourist, immigrant, or citizen of neighboring country).
Passenger model structure
A setup and analysis screen provides a quick overview of ICC operations and is sensitive to changes in demand
(passenger flow over time) scenarios. Analysts can test and determine the processes and facilities (number of booths,
scanners, parking places, etc.) needed to accommodate any number of passengers without causing downtime and/or long queues.
Setup and analysis screen by each type of passenger and controls
A separate passenger interface allows analysts to vary the number of cars and buses moving in each direction,
the number of passengers per vehicle, and the types of passengers moving in each direction to understand how
queues build and wait times change. They can then test operational and staffing level remedies.
The simulator also includes the control process for both local and international freight vehicles. Using actual
data and projections, it determines the number of entry lines, control booths, and physical review docks needed
to process each type of freight transit. Analysts can also experiment to determine how staffing levels influence
Freight setup and analysis screen
Using controls on the Expedited Dispatch Channels screen, analysts can set the average time needed for each freight
process per line. The simulator then displays the status of each process along with the number of vehicles in the
queue, the maximum waiting time, and the maximum vehicle load each hour.
Modeling insights and benefits
Using this simulator, ICC analysts have moved beyond reporting on transit processes to experimenting with modifications
to optimize each process and overall operations. “Managers are determining resource allocations according to traffic
flows expected on each shift over a 24-hour period,” says Sirca. “By opening the appropriate number of lines and
managing staffing levels, ICCs are avoiding bottlenecks and reducing queues.”
While the simulator has led to changes in ICC operations, Sirca doesn’t anticipate changes to the model itself.
“The model was built with sufficient flexibility and data to support even extreme scenarios for up to 20 years.
If and when it’s needed, we’ll be able to change the model to align with any modifications to the ICC concept,
its basic processes, or its layout.”
Story of the Month: Reissue
Our second Story of the Month reissue examines the complexities of energy prices. Can Energy Prices Really Be
Passed on to the Consumer? Energy literally fuels every aspect of today's economy. When energy costs increase,
many businesses will increase prices thereby "passing on" the cost to consumers. This story helps to tell
whether it is really possible.
The Story of the Month series was originally issued starting in May of 2001. While many things have changed
since then, many of the issues remain relevant. From corporate corruption, to terrorism, to greenhouse gasses,
each story analyzed a past headline news topic from a systems thinking perspective. These topics were modeled
using STELLA or iThink with the hopes to gain perspective on the system, stimulate discussion and perhaps
adjust our assumptions. isee systems will slowly be re-releasing each Story of the Month from our archives,
as originally developed, with an easy-to-access isee NetSim model.
Click Here to Run the Simulation!
Systems Thinking at Large
The Dynamics of a Keystone Species: The Reintroduction of Wolves to Yellowstone National Park
Keystone species are a fascinating aspect of an ecosystem. Like the keystone of an arch, this species forms
a central element to the whole system, enabling the ecosystem to function in a balanced state. As such an
important feature of an ecosystem, it begs the question: What would happen if a keystone species were removed?
How would the ecosystem react and what changes would take place? Would it be possible for another species
to fill the void or would the dynamics change altogether?
The dynamics of a keystone species can be examined by looking at the wolves of Yellowstone National Park.
Thought to be a menace by ranchers and farmers for killing livestock and with fears that wolves would harm
or kill humans, a large extermination of wolves occurred in the late 1800s and early 1900s. Almost eradicating
wolves altogether, the last wolf in Yellowstone was killed in 1927. During their almost 70-year absence, the
ecosystem changed dramatically as populations of herbivores were not kept in check and a cascade of
Systems Thinking at Large examines the wolves of Yellowstone and what happened to the ecosystem when the wolves
disappeared. This model, built in STELLA, uses storytelling to understand the dynamics of this keystone species.
What animals were affected by their presence or absence? See how wolves play a part in not only population control
of their prey, but other animals and even plants far down the trophic levels. This model offers a simplified
overview of an ecosystem and by no means encompasses all the aspects that were affected by the absence of wolves.
We hope you are able to gain insight from this general look into the dynamics of a keystone species, that can be
valid for different species in ecosystems all over the planet.
to view and run the simulation!
Community Model Building
On Thursday May 21st, we had our first community model building session! For this pioneer event, we
invited people to contribute in a discussion and model building session on the drought currently
affecting California. We were absolutely overwhelmed with the incredible response we received for this
community model building session! Over 160 people from all over the world registered for this event
and so many participated in the discussion it was a challenge for us to keep up with their suggestions.
Based on the feedback from the participants, we focused in on water usage and agriculture. In our one-hour
discussion with this community, we not only identified key variables that affected the focus area, but also
discussed the variable behavior and created an interesting causal loop diagram showing largely balancing
feedback loops. While the group discussion was active, co-president Bob Eberlein was actively
modeling the comments and suggestions we received from the community, resulting in a model that
showed the relationships between water supply, agricultural crop demand, crop price, and population.
The recording and results for this community build session will be available for viewing on June 9th, so be
on the look out!
We were so pleased with the participation from the community and we look forward to continuing
these community model building sessions in the future! If there is a particular complex issue you would
like to see modeled as a community please let us know!
Watch the full webinar in the video below!
On the Road!
It is that time of year! The 33rd International Conference of the System Dynamics Society will be
hosted this year in Cambridge, Massachusetts from July 19th to July 23rd. isee systems will once
again be sponsoring and attending this annual event. This is an exciting time for us to meet and
talk with our customers and Systems Thinking practitioners as we have just released the 10.1 upgrade
to STELLA/iThink and our brand new product, Stella Professional 1.0! Stop by our booth
to meet members of our team, see a demo of the new software, and get a sneak peak at what’s to
come! We will be available throughout the conference to answer your modeling questions, learn
about your project as well as listen to what you would like to see improved in our software.
Co-presidents Karim Chichakly and Bob Eberlein will be presenting the 9th Barry Richmond
Scholarship Award to a Systems Thinking practitioner whose work demonstrates a desire to
expand the field or to apply it to current social issues.
Finally, co-president Bob Eberlein and software developer Billy Schroenberg will be conducting
two workshops during this conference. They are Getting Started with Stella Professional and
Using modules and arrays with Stella Professional. To learn more on these workshops visit
the System Dynamics Conference webpage at www.conference.systemdynamics.org.
We look forward to seeing you all there!
STELLA/iThink 10.1 – The bridge to the future of modeling
Version 10.1 comes with exciting new features and yet remains the trusted modeling software that you
are used to. Stella LiveTM allows you to see modeling results of stocks and flows directly in the diagram.
They are instantly updated as you dial up or down constants in the model. Cycle time, allowing you to
time stamp and track material in your model, and Sketchable Graphs, enabling you to sketch expected
behavior, have been reintroduced.
Learn more about STELLA/iThink 10.1!
New Sensitivity analysis is now available for Monte Carlo simulations. Now table settings can vary from
table to table.
Stella Professional - The next generation in modeling
Stella Professional has been rebuilt from the ground up and takes your modeling experience to a higher
level. Now you can build models even more efficiently and get a fresh professional look. Models can be
kept clean and organized by resizing objects, using smooth Bezier connectors, and by allowing for
unlimited control over color, font, and title alignment. Tool bars can be detached and docked to wherever
you need them to improve your work flow. A new results panel enhances the effectiveness of your model analysis.
Equation and unit errors are summarized in a list so that you can solve any problems more quickly. Stella
Professional is the software that you know and love – with the new professional look and functionality that
you have been waiting for!
Learn more about Stella Professional!
Click the video below to watch the "Getting Started with Stella Professional Version 1" webinar!
Which software will fit your needs best?
Stella Professional makes it even easier to build and learn from your models. Currently, it comes without
an interface layer. To present and publish your models, you can easily open any Stella Professional file in
STELLA / iThink 10.1.
Learn more about the differences between STELLA/iThink 10.1 and Stella Professional
New Special Bundles!
This May, we are excited to introduce two new bundles that will help jumpstart your dynamic modeling project!
The Modeling Support Bundle and the From Systems Thinking to Dynamic Modeling Bundle!
Have you thought about a problem you would like to model, but do not know where to start? We can help!
Our new Modeling Support Bundle gives you not only the tool to model your problem but guidance as well!
With this bundle, you will work one-on-one with one of our dynamic modeling professionals to understand
the problem, create a needs analysis, frame modeling questions in the language of stocks, flows, and
feedback loops, and begin constructing a map of the system. Starting with a minimum of eight hours of
professional support, this bundle will springboard you to building your dynamic model and gaining meaningful insight!
Our new From Systems Thinking to Dynamic Modeling Bundle is one that every new modeler should have! This bundle
combines all six courses in our series that will lead you from thinking about systems to creating simulatable models.
Broken out into three sections, Introduction to Dynamic Modeling I & II, Dynamic Modeling I & II, and Intermediate
Dynamic Modeling I & II, each section will build upon the information you have learned and guide you through more
advanced concepts. Each course includes four one-hour pre-recorded classes, handouts, sample models, and homework
that will help solidify your learning. By the end of this series you will have the knowledge and confidence to
begin modeling and exploring dynamic systems. This bundle will also have the option of adding a six-month STELLA
or iThink license to help facilitate your learning.