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THINKING IN SYSTEMSCHAPTER 1: THE BASICSDONELLA MEADOWS
WHAT IS A SYSTEM?“A system is an interconnected set of elementsthat is coherently organized in a way thatachieves something (function or purpose).”
WHAT MAKES A SLINKY BOUNCEUP AND DOWN? The answer clearly lies within the Slinky itself. The hands that manipulate it suppress or release some behavior that is latent within the structure of the spring. That is a central insight of systems theory. Once we see the relationship between structure and behavior, we can begin to understand how systems work.
THE BLIND MEN & THE ELEPHANTThe behavior of a system cannot be known just byknowing the elements of which the system is made.
DIGESTIVE SYSTEM TEETH INTERCONNECTIONS MOUTH • Physical flow of food • Regulating chemical signals STOMACH ENZYMESThe function of the digestive system is to break down food into itsbasic nutrients and to transfer those nutrients into thebloodstream (another system) while discarding unusable wastes.
A FOOTBALL TEAM COACH PLAYERS Interconnections • Rules of the game • Coach’s strategy • Player’s communications • Laws of physics that govern the motions of balls & playersBALL FIELDPurpose: Win games, have fun, make millions of dollars, or all of the above.
EXAMPLES OF SYSTEMS School Factory Solar System Tree Animal Forest
CHARACTERISTICS OF A SYSTEM• Integrity or wholeness• Adaptive• Resilient• Evolutionary• Goal-seeking• Self-preserving• Self-organizing
INTERCONNECTIONS• The relationships that hold the elements together• Many of the interconnections in systems operate through the flow of information. Information holds systems together and plays a great role in how they operate.
FUNCTION/PURPOSE• Function is used for a nonhuman system, and purpose for a human one. Many systems have both human and non-human elements• Purposes are deduced from behavior, not from rhetoric or stated goals
SYSTEMS WITHIN SYSTEMS S u Student Purpose: To get good grades b - s y University Purpose: To discover & preserve knowledge s t Professor Purpose: To get tenure e• Keeping sub-purposes and m overall system purposes in s harmony is an essential function of successful systems. Administrator Purpose: To balance the budget
IMPACT ON SYSTEM WHEN CHANGES ARE MADE The elements are the parts of the system we are most likely to notice. They are least important in defining the unique characteristics of the system. Changing elements has the least effect n the system If interconnections change, the system may be greatly altered.Function/purpose is the least obvious partof the system. It is the most crucialdeterminant of the system’s behavior.Changes in function or purpose can bedrastic / profound
STOCKS & FLOWS Ba th tub The water in a bathtub is stock Flows are filling and draining the bathtub• A Stock is the foundation of any system. Stocks are the elements of the system that you can see, feel, count, or measure at any given time.• Stock change over time through the actions of the flow.
STOCKS & FLOWS Bat ht ub ad ding wat er draining wa te r The faucet and the drain are flows
STOCKS & FLOWS Stock Inflow Outflow 1. Stocks are shown as boxes 2. The flows are arrow-headed pipes, leading into or out of the stocks. 3. The small T on each flow signifies a faucet. 4. The clouds stand for wherever the flows come from and go to (i.e. the sources and the sinks).
BEHAVIOR OVER TIME GRAPHS Draining Water level in tub when the plug is pulled 1: Bathtub 1: 30 1 1 1: 15 1 1 1: 0 0.00 7.50 15.00 22.50 30.00 Minutes 11:46 AM Fri, Feb 20, 2009 Water in bathtub• System thinkers use graphs of system behavior to understand trends over time, rather than focusing attention on individual events• Behavior-over-time graph is used to learn whether the system is approaching a goal or limit, and if so, how quickly.
UNDERSTANDINGBEHAVIOR OVER TIME Dynamic Equilibrium 1: Bathtub 1: 26 1: 25 1 1 1 1 1: 24 0.00 7.50 15.00 22.50 30.00 Minutes 11:34 AM Fri, Feb 20, 2009 Water in bathtub Principles • If the sum of all outflows equals the sum of all inflows, the stock level will not change; it will be held in dynamic equilibrium • As long as the sum of inflows exceeds the sum of all outflows, the level of stock will rise • As long as the sum of all outflows exceeds the sum of all inflows, the level of stock will fall
THE ROLE OF STOCKS IN SYSTEMS• A Stock takes time to change, because flows take time to flow.• Changes in stocks set the pace of the dynamics of systems.• Most individual and institutional decisions are designed to regulate levels of stock• System thinkers see the world as a collection of stocks along with the mechanisms for regulating levels in the stocks by manipulating flows.
OTHER STOCKS &FLOWS Ban k Acc ount C02 I n At mosp here mak in g d epo sits ad ding c0 2 Se lf E ste em bu ildin g Same thing, different units
FEEDBACK LOOPS A feedback loop occurs when a stock affects its flows Ban k acc oun t ea rn in g in teres t int erest rat e R• A Feedback loop is formed when changes in stock affect the flows into or out of that same stock. Example: Total amount of money in an account (stock) affects how much money comes into the account as interest.• Feedback loops can cause stocks to maintain their level within a range or grow or decline. The stock level feeds back through a chain of signals and actions to control itself.
FEEDBACK LOOPS 1. STABILIZING LOOPS - BALANCING FEEDBACK Energy Level of a Coffee Drinker The feedback loop can correct an oversupply or an undersupply• This kind of feedback loop stabilizes the stock level. It is stabilizing, goal seeking, regulating and is called a Balancing Feedback Loop.• The stock level may not remain completely fixed, but it does stay within an acceptable range.
HOMING BEHAVIOR OF THEBALANCING FEEDBACK LOOP Whatever the initial value of the system stock (coffee temperature in this case), whether it is above or below the “goal” (room temperature), the feedback loop brings it toward the goal. The change is faster at ﬁrst, and then slower, as the discrepancy between the stock and the goal decreases.
FEEDBACK LOOPS2. RUNAWAY LOOPS - REINFORCING FEEDBACK Population Bank acc ount births earning interest R R birth rate interest rate Reinforcing loops are found wherever a system element has the ability to reproduce itself or to grow as a constant fraction of itself. Those elements include populations and economies.
THINKING IN SYSTEMSCHAPTER 2: A BRIEF VISIT TO THE SYSTEMS ZOODONELLA MEADOWS
ONE-STOCK SYSTEMS A Stock with Two Competing Balancing Loops
ONE-STOCK SYSTEMSA Stock with One Reinforcing Loop and OneBalancing Loop—Population and Industrial EconomySHIFTING DOMINANCE OF FEEDBACK LOOPS: When one loopdominates another, it has a stronger impact on behavior. Because systemsoften have several competing feedback loops operating simultaneously,those loops that dominate the system will determine the behavior.
ONE-STOCK SYSTEMS A Stock with One Reinforcing Loop and One Balancing Loop—Population and Industrial EconomySystems with similar feedback structures produce similar dynamicbehaviors, even if the outward appearance of these systems is completelydissimilar.
ONE-STOCK SYSTEMS A System with Delays—Business InventoryDelays are pervasive in systems, and they are strong determinants ofbehavior. Changing the length of a delay may (or may not, depending on thetype of delay and the relative lengths of other delays) make a large changein the behavior of a system.
TWO-STOCK SYSTEMS A Renewable Stock Constrained by a Nonrenewable Stock — an Oil Economy Nonrenewable resources are stock-limited. The entire stock is available at once, and can be extracted at any rate (limited mainly by extraction capital). But since the stock is not renewed - the faster the extraction rate, the shorter the lifetime of the resource.
TWO-STOCK SYSTEMS Renewable Stock Constrained by a Renewable Stock— a Fishing Economy Renewable resources are ﬂow-limited. They can support extraction or harvest indeﬁnitely, but only at a ﬁnite ﬂow rate equal to their regeneration rate. If they are extracted faster than they regenerate, they may eventually be driven below a critical threshold and become, for all practical purposes, nonrenewable.
SYSTEMS SURPRISE US BECAUSE…1. We pay too little attention to history. We are too fascinated by the events they generate (pp.90)2. We are not too skilled in understanding the nature of relationships (pp.91) as the world is full of nonlinearities.3. Beware of clouds! They are prime sources of system surprises.4. We get attached to the boundaries our minds happen to be accustomed to – often these boundaries are too large or too narrow (pp.98)5. Our minds like to think of single causes neatly producing single effects6. We don’t recognize which factor is limiting. Growth depletes or enhances limits and therefore changes what is limiting. (pp. 102)7. We rarely see the full range of possibilities before us (pp. 106). We are subject to bounded rationality i.e. we make reasonable decisions based on the information we have.