2 Jay Forrester (1918–2016)

In the 1950s, Jay Forrester, a systems engineer at MIT [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] , was commissioned by the US company Sprague Electric to study the extreme oscillations of their sales and establish a means to correct them. From previous experience, Forrester knew the essence of the problem stemmed from the oscillations present in situations that contain inertia effects, or delays and reverse effects, or feedback loops as basic structural characteristics.

Subsequently, in 1961, Forrester published his report on industrial dynamics that marked the beginning of the Systems Dynamics (SD) technique based on the study and simulation of the behaviour of social systems.

The experiences of Forrester that gave rise to the development of SD have been investigated in considerable detail by Brian Bloomfield (1986) as part of his PhD research with the Systems Group at The Open University. He describes the SD approach as:

Bloomfield does not regard SD as mere technique, but as a systems philosophy because it embodies a theory about the nature of complex feedback systems. This theory holds that people live in a network of feedback structures, incorporating economic, political and ecological subsystems. The feedback structures determine many of the problems – from famine to overcrowding, and inflation and unemployment to ecological collapse – which have caused considerable public concern in recent times (e.g. Figure 2 models unemployment and profit).

Forrester has been and remains a powerful figure in the SD community, which is regarded by many as somewhat closed.

Forrester, an electrical engineer by initial training, spent the years of the Second World War at MIT where feedback theory was being developed for the control of military equipment. In 1947, Forrester took charge of the MIT digital computer laboratory, which developed one of the first high-speed digital computers. The second phase of Forrester’s career began in 1956 when he moved into the field of management science at MIT’s Sloan School of Management. At the time, the mathematical approach of operations research was restricted to linear relationships between variables. This was because non-linear relationships could not be solved analytically. In contrast, Forrester advocated a closed-loop approach in which a feedback loop is established between policy output and information input (Bloomfield, 1986, p. 4).

Forrester published World Dynamics in 1968 and this served as a basis for the Meadows and Meadows (1972) report to the Club of Rome entitled Limits to Growth. Francois (1997) suggests the report and the extensive controversy it provoked were actually responsible for popularising SD. The cultural background as well as some of the methodological assumptions of SD have been heavily criticised (e.g. Flood and Jackson, 1991). Flood (1999), for example, suggests SD practice is open to criticisms of being imprecise because it relies on extant data and the outputs are potentially very sensitive to initial starting conditions, including assumptions. Many however find it useful.

Figure 2 The contribution of systems dynamics is exemplified by showing that the inadequate diagram of one-way, straight-line thinking is only part of the story. The closed-loop diagram used in SD modelling raises awareness of unintended consequences. In this case, it suggests the laying off of workers causes demoralisation of remaining workers and reduces productivity. (Downsizing is a management term for cutting staff to reduce company costs and raise profits.)

The initial stages in making an SD model involve the description of ‘the system’, identification of elements and relationships followed by the construction of a causal loop diagram (see Figure 2). SD has also developed its own modelling language and symbols, which are shown in Figure 2. (These multiple cause diagrams were introduced in Week 4 and are similar in principle to causal loop diagrams but use different conventions. In fact causal loop diagrams are more similar to sign graphs – a diagram type that has not been mentioned in this course but which you may come across.) It is argued by some that when engaging with complex situations many SD practitioners enable participants to learn just as much from the process of developing causal loop diagrams as from the subsequent computer simulations.

The influence of Jay Forrester can be judged by the fact that there is a thriving Systems Dynamics Society.