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Systems Thinking for Safety/Principle 7. Trade-offs
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People have to apply trade-offs in order to resolve goal conflicts and to cope with the complexity of the system and the uncertainty of the environment
Consider how people make trade-offs from their point of view and try to understand how they balance efficiency and thoroughness in light of system conditions
Work in complex systems is impossible to prescribe completely for all but fairly routine situations. Demand fluctuates, resources are often suboptimal, performance is constrained, and goals conflict. A busy airport that schedules traffic to a level near capacity leaves little room for disruption and requires consistently efficient performance. A lack of spare parts for equipment makes the functions vulnerable and may require workarounds. Often, the choices available to us are not ideal. We have to make trade-offs and choose among sub-optimal courses of action. This view contrasts with the simplistic view of prescribed work and non-compliance.
There are several different types of trade-offs, but a fundamental type is the ‘efficiency-thoroughness trade-off’ (ETTO; Hollnagel, 2009). Variations in system conditions (demand and pressure, resources, constraints) often create a need for efficiency over thoroughness. To achieve efficiency, we limit planning, quickly collect information and assess situations, make decisions on recognition of symptoms and ‘gut feeling’, enter data more rapidly, ‘multitask’, speak more quickly, reduce checking, and so on. The morning peak in traffic, limited time available for a software update or engineering work, or an urgent management decision, all call for greater efficiency. ETTO helps to frame how people and organisations try to optimise performance; people try to be as thorough as necessary, but as efficient as possible.
The possibility to switch successfully to a more efficient mode requires that at one time thoroughness was favoured over efficiency – a ‘TETO’ (thoroughness- efficiency trade-off). A system has to balance its resources and constraints dynamically to cope with complexity.
The efficiency-thoroughness trade-off has implications for understanding systems because it underlies all forms of work. It offers a useful alternative to ‘human error’ and is essential to help understand work-as-done.
As an example, what we may call an ‘expectation bias’ in hindsight is actually just an expectation, and one that is probably valid most of the time. Taking away the ‘bias’ would also make the task almost impossible, at least at anything like an acceptable level. Imagine the effect on the readback-hearback process if a controller had no idea what to expect in the readback. Readbacks are correct or acceptable in the majority of cases, so attention is split between the readback and other activities such as monitoring displays, recording flight data, and so on. The same can be said of rapid situation assessment and rapid decisions. If decisions in fast-paced environments were slow and deliberate, the task as we know it would be impossible. Trade-offs are essential for normal work.
Variable demands, production pressure and conflicting goals mean that people have to perform multiple activities in a given time frame, switching from one to another. This has several consequences. While some activities are sometimes amenable to ‘multi- tasking’, the conditions can make performance worse. Understanding how people switch between activities to achieve their goals is important to make sense of the situation from their points of view.
Other trade-offs involve short- vs long-term planning and sharp- vs blunt-end perspectives. For instance, additional resources may have to be deployed before the system runs out of capacity in face of rising demands. This may require shifting attention and resources to the longer term.
Trade-offs occur in all forms of work, in all organisational functions. Trade-offs must be considered from a system perspective, with the right view of the person, especially in light of system conditions. Doing so will help to understand system behaviour and system outcomes.
- Take the field experts’ perspectives. Data collection and interpretation are limited to what field experts can tell us. Assume goodwill and seek to understand their local rationality to consider how people make trade-offs from their point of view, balancing efficiency and thoroughness in light of system conditions.
- Get ‘thick descriptions’. A thick description of human behavior (Geertz, 1973) is one that explains not just the behavior, but its context as well, such that the behavior becomes meaningful to an outsider. This comprises not only facts but also commentary and interpretation by field experts. Use these thick descriptions in investigations of routine work and adverse occurrences.
- Understand the system conditions. Use observation and discussion to understand how and when trade-offs occur with changes in demands, pressure, resources and constraints.
View from the field
Philip Marien Incident Investigator EUROCONTROL & Editor of The Controller magazine, IFATCA
“Controllers and other front-line staff constantly make very specific assessments of situations to meet the demands of the system: ‘If I do this, what will be the outcome?’ In doing this, they constantly balance different goals; a priority one moment may not be a priority the next. It is naive to believe that these judgements always place applicable procedures, including separation standards, above everything else. Demands and pressures from pilots, colleagues, supervisors, management, etc, mean trade-offs are necessary. Too often, demands from higher up within an organisation rely too much on the front-line being able to find the right balance under all circumstances. This places a controller between a rock and a hard place because compromises that satisfy all goals are not possible. When the outcome is outside agreed standards, it’s (too) easy to focus on one aspect of the trade-off. Instead, we should address why achieving balance between the different goals is not always possible.”
- Geertz, C. (1973). The interpretation of cultures Chapter: Thick descriptions: Toward an interpretive theory of culture. pp. 301-323.
- Shorrock, S. and Licu, T. (2013): Target culture: lessons in unintended consequences . Hindsight 17, Summer 2013, pp. 10-16.
- Shorrock, S. and Licu, T. (2013): Target Culture: How Do Numerical Targets Affect Safety? presentation
- The ETTO Principle: Efficiency-Thoroughness Trade-Off Erik Hollnagel, 2013
Source: Systems Thinking for Safety: Ten Principles. A White Paper. Moving towards Safety-II, EUROCONTROL, 2014.
The following Systems Thinking Learning Cards: Moving towards Safety-II can be used in workshops, to discuss the principles and interactions between them for specific systems, situations or cases.