Weight loss

The definitions or measurement characteristics for overweight and obesity have varied over time, from study to study, and from one part of the world to another. The varied definitions affect prevalence statistics and make it difficult to compare data from different studies. Prevalence refers to the total number of existing cases of a disease or condition in a given population at a given time. Some overweight- and obesity-related prevalence rates are presented as crude or unadjusted estimates, while others are age-adjusted estimates. Unadjusted prevalence estimates are used to present cross-sectional data for population groups at a given point or time period, without accounting for the effect of different age variations among groups. For age-adjusted rates, statistical procedures are used to remove the effect of age differences when comparing two or more populations at one point in time, or one population at two or more points in time. Unadjusted estimates and age-adjusted estimates will yield slightly different values.

Previous studies in the United States have used the 1959 or the 1983 Metropolitan Life Insurance tables of desirable weight-for-height as the reference for overweight.[3] More recently, many Government agencies and scientific health organizations have estimated overweight using data from a series of cross-sectional surveys called the National Health Examination Surveys (NHES) and NHANES. The National Center for Health Statistics (NCHS) of the Centers for Disease Control and Prevention (CDC) conducted these surveys. Each had three cycles: NHES I, II, and III spanned the period from 1960 to 1970, and NHANES I, II, and III were conducted in the 1970s, 1980s, and early 1990s. Since 1999, NHANES has become a continuous survey.

source http://win.niddk.nih.gov/statistics/index.htm#table