Validation of obesity based on self-reported data in Spanish women participants in breast cancer screening programmes.
BACKGROUND
Measurement of obesity using self-reported anthropometric data usually involves underestimation of weight and/or overestimation of height. The dual aim of this study was, first, to ascertain and assess the validity of new cut-off points, for both overweight and obesity, using self-reported Body Mass Index furnished by women participants in breast cancer screening programmes, and second, to estimate and validate a predictive model that allows recalculate individual BMI based on self-reported data.


METHODS
The study covered 2927 women enrolled at 7 breast cancer screening centres. At each centre, women were randomly selected in 2 samples, in a ratio of 2:1. The larger sample (n = 1951) was used to compare the values of measured and self-reported weight and height, to ascertain new overweight and obesity cut-off points with self-reported data, using ROC curves, and to estimate a predictive model of real BMI using a regression model. The second sample (n = 976) was used to validate the proposed cut-off points and the predictive model.


RESULTS
Whereas reported prevalence of obesity was 19.8%, measured prevalence was 28.2%. The sensitivity and specificity of this classification would be maximised if the new cut-off points were 24.30 kg/m2 for overweight and 28.39 kg/m2 for obesity. The probability of classifying women correctly in their real weight categories on the basis of these points was 82.5% in the validation sample. Sensitivity and specificity for determining obesity using the new cut-off point in the validation sample were 90.0% and 92.3% respectively. The predictive model for real BMI included the self-reported BMI, age and educational level (university studies vs lower levels of education). This model succeeded in correctly classifying 90.5% of women according to BMI categories, but its performance was similar to that obtained with the new cut-off points.


CONCLUSIONS
Quantification of self-reported obesity entails a considerable underestimation of this problem, thereby questioning its validity. The new cut-off points established in this study and the predictive equation both allow for more accurate estimation of these prevalences.
Cancer and Environmental Epidemiology Unit, National Centre for Epidemiology, Carlos III Institute of Health, Madrid, Spain.
Beatriz
B
Isidoro
Virginia
V
Lope
Carmen
C
Pedraz-Pingarrón
Francisca
F
Collado-García
Carmen
C
Santamariña
Pilar
P
Moreo
Carmen
C
Vidal
María Soledad
MS
Laso
Milagros
M
García-Lopez
Marina
M
Pollán
D000368:Aged; D015992:Body Mass Index; D001943:Breast Neoplasms / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008403:Mass Screening; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology*; D015995:Prevalence; D012372:ROC Curve; D057566:Self Report / Q000592:standards*; D013030:Spain / Q000453:epidemiology