You are thinner than you think. (PART 1)

Accuracy of body size estimation: Role of biopsychosocial variables

Accuracy of body size estimation: Is it perceptual or emotional in nature?

Perceptual disturbances of body image are characterized by inaccurate perceptions, resulting in the reporting of an overestimation or underestimation of the size of body regions or of the whole body image. Although primarily investigated among eating disordered populations, the research on perceptual accuracy among normal populations (particularly women) has been an area of growing interest. The findings from the research have implications for the identification, prevention and treatment of body image disturbances.

Most previous research on body image has investigated the factors that may be associated with body image dissatisfaction, that is a subjective assessment of the level of satisfaction with one's current size or shape. Several variables have been implicated in the research on body image dissatisfaction, but the impact of these factors on estimates of body size has not been explored. These factors loosely fit into a biopsychosocial model of body image disturbance. The current study was designed to investigate the validity of this model in the prediction of accuracy of body image estimation, which is the extent to which one overestimates or underestimates the size of one's body. The major factors in the biopsychosocial model investigated in the current study included body mass index (BMI), depression and messages from peers and the media about the person's body.

It is proposed that the perception of body image results from two important processes. Firstly, perception of the physical dimensions of the body is achieved through the reception and integration of a variety of sensory inputs, including those of a visual, tactile and kinaesthetic nature. Perception of body image and its distortion may result from sensory factors such as stimulus intensity, visual deficiencies and attentional factors. Secondly, non-sensory factors may contribute to the perception of body image. These non-sensory factors include cognitive and affective factors based on an individual's beliefs, schemas and prior knowledge about one's body.

Previous studies have employed control objects, where participants estimate the dimensions of a box or a block of wood, as well as representations of themselves. In the current study, a vase was used to control for perceptual estimation errors due to factors unrelated to the perception of one's own body. It was expected that respondents would evidence higher levels of estimation inaccuracies for their bodies than for the vase.

Inconsistencies within the research on estimation accuracy of body image have been linked to the varying techniques employed to assess this construct. Some researchers have reported that both men and women overestimate (i.e., report their body to be larger than its actual size) body size with site-estimation techniques and underestimate (i.e., report their body to be smaller than its actual size) with whole-body procedures. Improving upon the limitations of previous techniques, a new computer-generated technique has been developed, which will be employed in the current study. Presented with a whole body image, the technique allows, within a single trial, the independent manipulation of five regions of the body (chest, waist, hips, thighs and calves).

The research has revealed inconsistent results with regard to the relationship between BMI and the accuracy of estimating body size. While some research has suggested that the accuracy of body size estimation is significantly related to the BMI of individuals who fall within a normal weight range, other studies have found that BMI values are not related to estimation accuracy. Studies have revealed that overweight men and women tend to underestimate their body size, while normal and underweight men and women estimated themselves to be larger than they actually were. A possible explanation as to why the accuracy of body size estimations vary in relation to BMI is that individuals attempt to bring their body size closer to average body size. On the other hand, some researchers have found that both over- and under-weight individuals have a tendency to overestimate their body size. The contradictions and inconsistencies throughout the research may be due to methodological differences, such as samples comprising more women than men, or different methods of measurement.

Persons with low mood have an increased tendency to attend to negative body information and evaluate their body more negatively, resulting in estimation inaccuracy in body size. Within a sample of women with no history of eating disorders, depressed mood was related to body size overestimation.

The degree of perceptual inaccuracy of specific regions of the body may vary according to the importance placed on them from sociocultural messages. A preoccupation with body image, transmitted socioculturally via the media, family and peers has been implicated in the etiology of body image disturbances and can affect how one cognitively and affectively responds to their body. Western culture values an increasingly thinner, ectomorphic female body ideal. With regard to the male ideal body image, sociocultural influences promote a large and muscular, mesomorphic, V-shaped body, which is stereotypically associated with masculinity, power and strength.

Within this framework, it would be expected that men would be more likely to demonstrate estimation inaccuracy in regions that are involved in the definition of the sociocultural ideal of a male body, such as the chest and upper torso area in particular. Women, on the other hand, would be expected to demonstrate inaccuracy in areas such as the mid and lower torso. Both men and women significantly overestimated body size, with men markedly overestimating the chest region, and women primarily overestimating the waist region. Men chose an ideal body that was 28 lb more muscular than themselves.

Other research findings have been less consistent, with no reported significant differences between men and women in the degree of estimation accuracy of the various body regions. A significant overestimation of the lower torso relative to the upper torso among women, whereas no such distinction in overestimation was found with men. Both men and women overestimated the waist, buttocks and thighs, with women overestimating these areas more than men, whereas women in the study overestimated their shoulders and thighs. Even brief exposure to muscular images resulted in an increased level of inaccuracy in the estimation of body size among men. These results suggest that the overestimation of body size in men and women may bring men closer to the sociocultural ideal for men, but take women further away from the sociocultural ideal for women.

The present study utilized a whole-body technique, where a distorted image of the individual's own body was presented, allowing them to adjust individual body parts. The degree of estimation accuracy was measured by the percentage of overestimation and underestimation. This technique is superior to former methods, as it allows individuals to make the images wider or thinner an unlimited number of times, until they are satisfied that the image represents their ‘actual’ size. The study compared the degree of estimation accuracy for specific body parts with the degree of estimation accuracy for the equivalent regions of an inanimate object, that is, a vase. It was expected that there would be better estimation accuracy for the vase. The inclusion of the vase acted as a control object to control for perceptual errors inherent in the task, but unrelated to one's body size. The biopsychosocial factors were BMI, depression, peer, and media influences to change weight. In keeping with the biopsychosocial model that has been developed to explain body dissatisfaction, it was predicted that BMI, depression and messages from the media and peers to lose weight and increase muscles would predict estimation accuracy for body size for men and women. These predictors were expected to be greater for men for the upper body, and for women for the lower body.

It was expected that men would be more likely to demonstrate estimation errors in the chest region, while women would be more likely to demonstrate estimation errors in the waist, hip and thigh regions. Men and women with a high BMI were also expected to demonstrate higher levels of estimation inaccuracy. It was also expected that both men and women with higher levels of depression would display higher levels of estimation inaccuracy. It was expected that there would be a higher levels of estimation inaccuracy for the various parts of the body compared to the vase. It was also expected that the level of estimation accuracy would be predicted by messages about ideal body size from the media and peers.