Obesity among women is derived from the Behavioral Risk Factor Surveillance Survey (BRFSS). The BRFSS is a health survey conducted by 50 states, 3 territories, and the District of Columbia, and is the primary source of information on health-related behaviors of Americans. Questions are related to chronic diseases, injuries, and infectious diseases that can be prevented. States use standard procedures to collect data through a series of monthly telephone interviews with adults. The BRFSS questionnaire is developed jointly by Centers for Disease Control and Prevention and state health departments and includes five sections. Obesity is part of a standard core of questions asked every year.
Methodological changes to the BRFSS in 2011 have affected the trends in prevalence estimates and they are not comparable to earlier years. The changes include the addition of cellular phones and improvements in the statistical weighting methods. More info can be found on the CDC Web site.
Calculations for BRFSS Obesity indicators are performed by the March of Dimes Perinatal Data Center, and include the percent of women of childbearing age (18-44 years) defined by BRFSS to be obesity. Body Mass Index (BMI) is a number calculated from a person's weight and height. Obesity is defined as persons who have a Body Mass Index of 30 or more. US rate is the median of states which reported that year. More background can be found on the BRFSS Web site.