for Drawing Causal Loop Diagrams 1
by Daniel H. Kim
The old adage
"if the only tool you have is a hammer, every-thing begins
to look like a nail" can also apply to language. If our language
is linear and static, we will tend to view and interact with our
world as if it were linear and static. Taking a complex, dynamic,
and circular world and linearizing it into a set of snapshots
may make things seem simpler, but we may totally misread the very
reality we were seeking to understand. Making such inappropriate
simplifications "is like putting on your brakes and then
looking at your speed-ometer to see how fast you were going,"
says Bill Isaacs of dialogos.
Causal loop diagrams provide a language for articulating our understanding
of the dynamic, interconnected nature of our world. We can think
of them as sentences which are constructed by linking together
key variables and indicating the causal relationships be-----tw-een
them. By stringing together several loops, we can create a coherent
story about a particular problem or issue.
The next page includes some suggestions on the mechanics of creating
causal loop diagrams. Below are some more general guidelines that
should help lead you through the process:
Theme Selection. Creating causal loop diagrams is
not an end unto itself, but part of a process of articulating
and communicating deeper insights about complex issues. It is
pointless to begin creating a causal loop diagram without having
selected a theme or issue that you wish to understand better.
"To understand the implications of chang-ing from a technology-driven
to a marketing-oriented strategy," for ex-ample, is a better
theme than "to better understand our strategic planning process."
Time Horizon. It is also helpful to determine an
appropriate time horizon for the issue-one long enough to see
the dynamics play out. For a change in corporate strategy, the
time horizon may span several years, while a change in advertising
campaigns may be on the order of months.
Time itself should not be included as a causal agent, however.
After a heavy rainfall a river level steadily rises over time,
but we would not attribute it to the passage of time. You need
to identify what is actual driv-ing the change. In manufacturing,
for example, costs of a new product often decline over time. It
would be incorrect, however, to draw a causal connection between
time and unit costs. Instead, process improvements and learning
curve effects are likely causal forces.
Behavior Over Time Charts. Identifying and drawing
out the behavior over time of key variables is an important first
step toward articulating the current understanding of the system.
Drawing out future behavior means taking a risk-the risk of being
wrong. The fact is, any projection of the future will be wrong,
but by making it explicit, we can test our assumptions and uncover
inconsistencies that may otherwise never get surfaced. For example,
drawing projections of steady productivity growth while training
dollars are shrinking raises the question "If training is
not driving productivity, what will?" The behavior over time
diagram also points out key variables that should be included
in the diagram, such as training budget and productivity. Your
diagram should try to capture the structure that will produce
the projected behavior.
Boundary Issue. How do you know when to stop adding
to your diagram? If you don't stay focused on the issue, you may
quickly find yourself overwhelmed by the number of connections
possible. Remember, you are not trying to draw out the whole system-only
what is critical to the theme being addressed. When in doubt about
including something, ask, "If I were to double or halve this
variable, would it have a significant effect on the issue I am
mapping?" If not, it probably can be omitted.
Level of Aggregation. How detailed should the diagram
be? Again, this should be determined by the issue itself. The
time horizon also can help determine how detailed the variables
need to be. If the time horizon is on the order of weeks (fluctuations
on the production line), variables that change slowly over a period
of many years may be assumed to be constant (such as building
new factories). As a rule of thumb, the variables should not describe
specific events (a broken pump); they should represent patterns
of behavior (pump breakdowns throughout the plant).
Significant Delays. Make sure to identify which
(if any) links have significant delays relative to the rest of
the diagram. Delays are important because they are often the source
of imbalances that accumulate in the system. It may help to visualize
pressures building up in the system by viewing the delay connection
as a relief valve that either opens slowly as pressure builds
or opens abruptly when the pressure hits a critical value. An
example of this might be a delay between long work hours and burnout:
after sustained periods of working 60+ hours per week, a sudden
collapse might occur in the form of burnout.
See Guidelines and Examples (page
was originally published in The Systems Thinker, Volume
3, Number 1.
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