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The Language of Systems Thinking: "Links" and "Loops"
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The Language of Systems Thinking: "Links" and "Loops"

Michael Goodman, Jennifer Kemeny, Charlotte Roberts

In systems thinking, every picture tells a story. From any element in a situation (or "variable"), you can trace arrows ("links") that represent influence on another element. These, in turn, reveal cycles that repeat themselves, time after time, making situations better or worse.

This image, for instance, from the Acme Company, shows the level of service influencing sales. Everv time service grows poorer (when billing and delivery problems increase), sales will also decrease. Conversely, if the level of service improves, we can expect (eventually, at least) more sales.

But links never exist in isolation. They always comprise a circle of causality, a feedback "loop," in which every element is both "cause" and "effect" influenced by some, and influencing others, so that every one of its effects, sooner or later, comes back to roost.

How to Tell the Story from a Loop

Start anywhere. Pick the element, for instance, of most immediate concern.
Any element may go up or down at various points in time. What has the element been doing at this moment? Try out language which describes the movement: As Acme's sales level goes up . . . goes down . . . improves . . . deteriorates. . . increases. . . decreases. . . rises. . . falls . . . soars . . . drops. . . waxes . . . wanes . . .
Describe the impact this movement produces on the next element As Acme's sales level goes down, the number of efforts to sell new accounts goes up.
Continue the story back to your starting place. Use phrases that show causal interrelationship: "This in turn, causes . . ." or ". . . which influences . . ." or ". . . then adversely affects . . ." As Acme's sales level goes down, the number of efforts to sell new accounts goes up. This means the level of service drops, which in turn influences sales to continue falling . . .
Try not to tell the story in cut-and-dried, mechanistic fashion. When service problems rise, sales fall. As sales fall, sales force efforts rise. Instead, make it come alive. Add illustrations and short anecdotes so others know exactly what you mean.... This means the level of service drops. We just can't keep to the delivery schedules we promised. Loyal customers, in turn, become upset. Some stop doing business with us . . .
Note that linear languages, like English, permit us to talk about the loop only one step at a time, as if we were following a train in a toy railroad around a track. In reality, however, all of these events occur at once. Seeing their simultaneity (. . . sales continue to fall, while we spur even more efforts to sell new accounts . . .)  helps you recognize system behavior and develop a sense of timing.

Reinforcing Loops: when small changes become big changes

There are basically two building blocks of all systems representations: reinforcing and balancing loops.

Reinforcing loops generate exponential growth and collapse, in which the growth or collapse continues at an ever-increasing rate. To grasp the often-surprising ramifications of exponential growth, consider an interest-bearing bank account. Your money grows much faster than it would if you merely put $100 each year into a piggy bank. At first, the difference seems small, interest would generate only a few extra dollars per year. But if you left the interest in the bank, the money would grow at an ever-faster rate. After fifty years (at 7 percent interest), you'd have more than $40,000, more than eight times as much as the piggy bank would generate by growing at the same rate, year after year.

If you were unprepared for it, you'd reach a moment of surprise after perhaps fifteen vears, when you saw how the growth of your money was building on itselfa truly virtuous spiral.

But you'd be caught in a vicious spiral if, instead of investing money, you went into debt for a long time. At first it would seem as if you were paying only small sums in interest. But over time, the balance you owed would grow with increasing speed.

In all reinforcing processes, as in the bank account, a small change builds on itself. High birth rates lead to higher birth rates; industrial growth begets more industrial growth. Don't underestimate the explosive power of these processes; in their presence, linear thinking can always get us into trouble. For example, organizations often assume that they will face steady, incremental growth in demand. They are startled to discover that when their new facilities come on line (be they factories, distribution systems, utility grids, jails, highways, or city services) the demand has already overshot the relief effort.

When someone remarks that, "The sky's the limit," or "we're on a roll," or "This is our ticket to heaven," you can bet there's a reinforcing loop nearby, headed in the "virtuous" direction they prefer.

When people say, "we're going to hell in a handbasket," or "we're taking a bobsled ride down the chute," or "we're spiraling to oblivion," you know they're caught in the other kind of reinforcing loop -- the vicious cycle.

There can be any number of elements in a reinforcing loop all in a circle, all propelling each others' growth.

Reinforcing loop situations generally "snowball" into highly amplified growth or decline. If you wish, use the letter R  to mark a reinforcing loop.

A reinforcing loop, by definition, is incomplete. You never have a vicious or virtuous cycle by itself. Somewhere, sometime, it will run up against at least one balancing mechanism that limits it. The limit may not appear in our lifetime, but you can assume it will appear. Most of the time, there are multiple limits.


Balancing loops: pushing stability, resistance, and limits

Balancing processes generate the forces of resistance, which eventually limit growth. But they are also the mechanisms, found in nature and all systems, that fix problems, maintain stability, and achieve equilibrium. They ensure that every system never strays far from its "natural" operating range -- a human body's homeostatic state, an ecosystem's balance of predator and prey, or a company's "natural" expenses, which, whenever you cut them, seem to balloon up somewhere else.

Balancing loops are often found in situations which seem to be self-correcting and self-regulating, whether the participants like it or not. If people talk about "being on a roller coaster," or "being flung up and down like a yo-yo," then they are caught in one type of balancing structure. If caught in another type, they may say, "We're running into walls," or "We can't break through the barrier," or "No matter what we try, we can't change the system." Despite the frustration they often engender, balancing loops aren't innately bad: they ensure, for example, that there is usually some way to stop a runaway vicious spiral. Our survival depends on the many balancing processes which regulate the earth, the climate, and our bodies.

Balancing processes are always bound to a target -- a constraint or goal which is often implicitly set by the forces of the system. Whenever current reality doesn't match the balancing loop's target, the resulting gap (between the target and the svstem's actual performance) generates a kind of pressure which the system cannot ignore. The greater the gap, the greater the pressure. It's as if the system itself has a single-minded awareness of "how things ought to be," and will do everything in its power to return to that state. Until you recognize the gap, and identify the goal or constraint which drives it, you won't understand the behavior of the balancing loop.

The North Millerfield Community Hospital (a pseudonym) in Connecticut opened a very attractive outpatient clinic in the late 1980s. The administrators knew that it was meeting a real need, and they assumed it would always be filled with patients, almost up to its capacity. That would make it a constant revenue generator. However, a few months after it opened, the number of patient visits (and thus revenues) leveled off, below the hospital's forecasts. The hospital started a community marketing campaign, and patient visits rose for a time, but soon dropped off again.

Finally, the administrators took a close look at their patient volume statistics. They spent time in the waiting room and surveyed staff at the front desk and patients. It turned out that when traffic was low, people were served quickly. Word got around, doctors and paramedics referred people, and North Millerfield's clinic became crowded. But people have an innate distaste for sitting in busy waiting rooms. Since they had a choice, they went elsewhere. The general lesson for all businesses is: if you don't adjust your service satisfaction to the level expected by your customers, the system will do it for you!

Sometimes, the target is clearly articulated and shared. Everyone in a sales force knows their sales targets. Other times, it is obscure, ill-defined, implicit, or assumed. The level of quality which customers would accept has driven the changes in the auto industry for the past twenty years, but no one has been able to agree on, or measure, that level of quality. A vision may drive the behavior of a team but never be articulated. Sometimes the target moves or changes, because it too is subject to influences from the system. In fact, discovering or creating new targets is often the key to overcoming the resistance that confronts you.


Here is how you might represent North Millerfield's patient demand system in a balancing loop. Note that the comments in parentheses (Waiting time is "rising," while patient satisfaction is "going down") represent a snapshot of only one moment of the system. At other times during the clinic's more unpopular peliods, waiting time will fall, while patient satisfaction goes up.

We use a "balance beam" at the center of the loop, because it shows one common type of balancing loop behavior: "teeter-tottering" around a desired level, first overshooting a bit, then compensating in the other direction, and finally coming to rest at the target. If you prefer, label your balancing loops with the letter B.

Delays: when things happen . . . eventually

Delays occur often in both reinforcing and balancing loops. These are points where the link (the chain of influence) takes a particularly long time to play out. We represent delays with a pair of parallel lines.

Delay can have enormous influence in a system, frequently accentuating the impact of other forces. This happens because delays are subtle: usually taken for granted, often ignored altogether, always under-estimated. In reinforcing loops, delays can shake our confidence, because growth doesn't come as quickly as expected. In balancing loops, delays can dramatically change the behavior of the system. When unacknowedged delays occur, people tend to react impatiently, usually redoubling their efforts to get what they want. This results in unnecessarily violent oscillations. One of the purposes of drawing systems diagrams is to flag the delays which you might otherwise miss. In addition, delays are often a source of waste; removing delays is a key method for speeding up cycle time.

When drawing systems archetypes, you may choose to mark more than one delay. But it is most helpful to identify the most significant delays -- particularly the longest delays, relative to the other links.

For example, in the Nolth Millerfield Hospital story, there are at least two significallt delays:

The delay before customer satisfaction goes down. ("The first time I visited the clinic, I assumed the long waits were just a fluke. The second time I visited, I wanted to go somewhere else, but my spouse insisted.")
The delay before the impact is felt of the clinic's lost reputation. ("That was the end for us. We haven't been back in months. I drove by last week and noticed that they've started advertising for patients.")
The underlying dynamic, of course, applies not just to hospital emergency rooms, but to restaurants, fast-food windows, stores, supermarkets, banks, gas stations, government agencies, and anvone who drives away customers by missing a key component of good service.


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