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chapter nine Eating Disorders and Obesity: Epidemiology and the Perception of Risk Leora Pinhas, Hospital for Sick Children Benjamin Taylor, University of Toronto Risk is difficult to interpret and manage. Even for scientists and clinicians, understanding how risk impacts your life is nearly impossible given the widely varying, and often disparate, messages we receive. Additionally, realizing subtle differences in absolute risk (one’s overall chance of developing diabetes, for example) and relative risk (your change in diabetes risk due to a factor such as diet) are nearly impossible, particularly given the type and amount of information we receive. This chapter will provide a context with which to think about risk––from the sources of data to how it is presented and even how the subject matter impacts interpretation and meaning. Specifically, this chapter will focus on the literature and knowledge around obesity and eating disorders and finish with a discussion on how decisions about risk impact prevention and intervention in a clinical setting. Risk Risk is defined as a chance or possibility of danger, loss, injury, or other adverse consequence (Allen, 1990). However, in the technical language of epidemiology, risk is simply defined as the probability, or likelihood, that an event, whether positive or negative, will occur within a stated period of time or by a certain age (Last, 2001). Therefore, a risk factor is an attribute or exposure that is associated with an increased probability of a specified outcome. Therefore, we could speak about the risk of leg cramps following swimming, the risk of a hand injury when using a power drill, or the risk of sneezing after pepper exposure. Importantly though, we are not necessarily talking about a causal relationship, where one factor precedes 2 2 3 2 2 4 L e o r a P i n h a s , B e n ja m i n Ta y l o r the outcome and is required for that outcome to occur (Last, 2001). Often, when most people speak about risk, they might simply be referring to an association. This can be misinterpreted as causation. For example, women are at greater risk of getting breast cancer than men, but this does not mean that being a woman causes breast cancer. A cause is something that is necessary to produce an effect, while an association is present simply if the probability of an occurrence of an event depends on the occurrence of another event or characteristic, which may or may not be a causal relationship (Last, 2001). So, while being female does not cause breast cancer, there is an association between the two since being female does predict a higher risk of developing breast cancer than being male. Just by examining these definitions, it becomes clear that scientists and the lay public use the word risk to describe quite differing concepts. Absolute versus Relative Risk There are two main types of risk––absolute risk and relative risk––and although they are related they can often be wildly different for the same disease. Absolute risk is simply the incidence of a disease in a population. Relative risk is the probability of an event or outcome occurring in an exposed group (to some factor of interest) as compared to the probability of the event in non-exposed people (Gordis, 2004). We will look at an example of adolescent obesity prevalence to illustrate these two concepts. One of the concerns about obesity is the associated morbidity of certain illnesses such as diabetes. How data are presented can lead to confusion because of the misunderstandings that arise in relation to relative and absolute risk. Canadian incidence studies report that 95% of the new cases of type II diabetes in children and adolescents occur in obese youth (Canadian Paediatric Society, 2008). From these data, we can then say that the risk of type II diabetes is 19 times greater in obese children and adolescents as compared to non-obese youth. In fact, the authors of this study have recommended screening all obese youth for type II diabetes, despite the fact that there are only about 200 new cases per year in all of Canada (Canadian Paediatric Society, 2007). While most of these cases do occur in obese youth, the absolute incidence in obese youth is about 1 per 2,000 individuals (0.0005%) (Shields, 2004). This finding means that physicians would have to screen 1999 obese young people before they found one new case with type II diabetes. It is unlikely that any...

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