Adapted from Senge, P. et al. 1994, the fifth discipline field book, p. 113-120
In a feedback loop every element is both ‘cause’ and ‘effect’. For every variable you can trace links that represent influence on another element. This way cycles are revealed that repeat themselves. Figure X presents an example with increasing numbers of patients increasing waiting times in a clinic, and increasing waiting times leading to decreasing numbers of patients, leading to decreasing waiting times again, and so on.
Figure X: Example of a feedback loop
There are basically two building blocks of all systems representations:
- Reinforcing loops: generate growth and collapse, in which the growth or collapse continues at an ever-increasing rate. A small change builds on itself, resulting in big changes after some time. There can be any number of elements in a reinforcing loop, all propelling each others’ growth. Reinforcing loop situations generally “snowball” into highly amplified growth or decline. Somewhere sometime the reinforcing loop will run up against at least one balancing mechanism that limits it. The letter R is used to mark a reinforcing loop.
- Balancing loops: generate stability. Balancing processes generate the forces of resistance, which eventually limit growth. Balancing loops are found in situations which seem to be self-correcting and self-regulating. The letter B is used to mark a balancing loop.
In addition to feedback loops also time needs to be taken into account. Both in reinforcing and balancing loops delays may occur. Delays are the points where the link takes a particularly long time to play out. Delays can have enormous influence in a system, frequently accentuating the impact of other forces. When unacknowledged delays occur, people tent 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.