Cake or Fruit: Non-linearity in Decision-Making

Previously I’ve discussed the work of Resnicow and Vaughn (1), who suggest that traditional models of behaviour change fail to embrace the complexity of human behaviour. They call for a new paradigm to conceptualize behaviour change using a complex systems lens. As highlighted before, most traditional theories view behaviour change as linear and deterministic, they often assume homogeneity of the target population, feedback is often missing, and although they acknowledge multiple contributing factors, the interdependency of these factors is ignored.

Figure 1

Let’s explore the non-linearity of behaviour a little more closely, focusing on one characteristic of complexity.  Fitting a linear, deterministic model to human behaviour fails to address the complexity inherent in behaviour change. Consequences of this may limit the potential for success in interventions based on these models. In a system that is linear, x varies in proportion to y, as is illustrated in Figure 1.

In a dynamic system, this relationship is not linear – there are multiple possibilities. One example relevant to behaviour change is that of human decision making and how it varies over time. Dan Ariely discusses how time affects the decisions we make about healthy eating(2). For example, many of us decide that we want to eat healthy foods more often, such as choosing fresh fruit for dessert instead of chocolate cake. Yet we struggle to uphold these choices over time.

Before a meal, we have a stronger preference for fresh fruit over chocolate cake: fruit is healthier and the higher calories of a decadent dessert may contribute to unwanted weight gain. But our preferences change over time (Figure 2). When the time to have dessert arrives, our preference for cake increases, perhaps driven by hedonistic desires, and surpasses the reward value of the fruit. Later, after the meal is over, our preferences may change again. The cake no longer seems as appealing, perhaps we even regret the choice or feel guilt. As its reward value decreases over time, fruit again becomes preferable.

Figure 2: Non-linearity in human behaviour – how decisions vary with time (Adapted from Ariely, D. (2001). A timely account of the role of duration in decision making. Acta Psychologica, 108(2), 187-207)

This variability in our decision making over time can be applied to many other examples, such as evening plans to go for a walk versus watching TV. Even if we try to be more logical about decisions, by weighing the costs and benefits of the different options, the importance we place on the various costs and benefits also changes with time.

These examples clearly illustrate how human behaviour change does not fit a linear model, and highlight the need for a complex systems approach as called for by Resnicow and Vaughn. In future posts I’ll explore what this complex systems approach might look like, please stay tuned!

1. Resnicow K, & Vaughan R (2006). A chaotic view of behavior change: a quantum leap for health promotion. The international journal of behavioral nutrition and physical activity, 3 PMID: 16968551 2. Ariely D, & Zakay D (2001). A timely account of the role of duration in decision making. Acta psychologica, 108 (2), 187-207 PMID: 11569762 doi:10.1016/S0001-6918(01)00034-8

Photo Credit: Strawberry Sacrilege by Martin Newman.


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