The Harmful Fetishisation of Reductive Personal Tracking Metrics in Digital Systems

Personal tracking and the quantified self have grown increasingly popular as technological capabilities for individual insights have grown. Incorporated into many of these systems is the capacity to monitor metrics over time to offer visualisations of attributes such as health, fitness and nutrition. However, many such systems rely on single, simplified measures to represent these complex phenomena, and due to tracking and visualisations, they add value judgements, such as success and failure, to the users' information. This paper, therefore, aims to shed light on the challenges of reductive measures through the case of the BMI (Body Mass Index). The BMI is a clear example of a reductive measure that is used to offer insight into health in both formal and informal healthcare, despite a substantial body of literature that demonstrates other more accurate factors of health that are easily measured. Through a historical consideration of the origin and narratives around the BMI, we demonstrate the fallacy of its use and offer a broader critique of reductive metrics. This understanding of the BMI allows us to highlight the potential harms arising from personalised 'health' tracking technologies and the values encoded into such systems: we use established frameworks of digital harm to demonstrate that using the BMI is harmful for not only well-documented health reasons, but that this harm is exacerbated when it is incorporated into digital technology. Our paper offers a challenge to traditional health thinking and, more broadly, the fetishisation of reductive metrics in data systems.