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Section I - Part

Published online by Cambridge University Press:  04 September 2021

Jo. M. Martins
Affiliation:
International Medical University, Malaysia
Indra Pathmanathan
Affiliation:
United Nations University - International Institute for Global Health
David T. Tan
Affiliation:
United Nations Development Programme
Shiang Cheng Lim
Affiliation:
RTI International
Pascale Allotey
Affiliation:
United Nations University - International Institute for Global Health

Summary

Information

Figure 0

Table 2.1 The bathtub metaphor

Source: Newell (2012).
Figure 1

Figure 2.1 The susceptible–infected–recovered (SIR) system. This stock-and-flow map represents the causal structure of the system that governs the spread of infectious diseases. In epidemiological practice, this structure is known as the SIR model. The three stocks shown in the map are connected by two flows that represent the processes of infection and recovery, respectively. The rates of these state-change processes are controlled by the levels of the stocks.

Figure 2

Figure 2.2 A causal loop diagram (CLD). This diagram depicts the story of the fight against increasingly prevalent antibiotic-resistant bacteria. An increase in the incidence of serious bacterial infections leads to an increase in the volume of antibiotics prescribed. The prescription of antibiotics leads to a reduction in the incidence of serious infections. At the same time, however, the increased use of antibiotics increases the evolutionary pressure on bacterial populations, leading to an eventual increase in the richness and abundance of drug-resistant species and a consequent increase in the incidence of serious infections. While the latter effect takes time to appear, it eventually dominates.

Figure 3

Figure 2.3 Two types of feedback structure: (a) reinforcing feedback; (b) balancing feedback. In general, a dynamic hypothesis that aims to explain the behaviour of a real-world system will comprise a network of competing reinforcing and balancing loops.

Figure 4

Figure 2.4 An influence diagram (ID). This example represents a feedback loop where Time spent exercising affects Level of physical fitness. This change affects Enjoyment of exercise, which leads to a further change in Time spent exercising – and so on around the loop. IDs do not have polarities assigned to influence links.

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