Methods and Limitations
We estimated the distribution of age at diagnosis of diabetes using data from the National Health Interview Survey (NHIS) of the National Center for Health Statistics (NCHS), Centers for Disease Control and Prevention (CDC). Being conducted continuously since 1957, NHIS is a health survey of the civilian, noninstitutionalized, household population of the United States. The survey provides information on the health of the United States population, including information on the prevalence and incidence of diseases, the extent of disabilities, and the use of health care services. The multistage probability design of the survey is described elsewhere.1
Since 1997, adult respondents were asked whether a health professional had ever told them that they had diabetes. To exclude gestational diabetes, women were asked whether they had been told they had diabetes other than during pregnancy. Adults who reported being diagnosed with diabetes were then asked at what age they were diagnosed.
Age at diagnosis of diabetes was calculated among incident cases for adults aged 18–79 years. The survey data were not collected among people younger than 18 years, and there were limited data available for people aged 80 years and older.
Median ages at diagnosis are presented by sex and race/ethnicity. People of Hispanic origin may be of any race. The race groups include people of both Hispanic and non-Hispanic origin. Boxplots were constructed to display the distribution of age at diagnosis among incident cases for each year. Three-year averages were used to improve the precision of the annual estimates.
People with diabetes may have diabetes many years before diagnosis.2 Therefore, the NHIS may underestimate the true age at developing diabetes. With these cross-sectional data it is impossible to determine the causes of any changes, either increase or decrease, in the distribution of age at diagnosis of diabetes. There might be recall bias (people who have had diagnosed diabetes for a long time might not accurately recall the age they were when it was diagnosed).
- Botman SL, Moore TF, Moriarity CL, Parsons VL. Design and estimation for the National Health Interview Survey, 1995–2004. National Center for Health Statistics, Centers for Disease Control and Prevention. Vital and Health Stat. 2000;130.
- Harris MI, Klein R, Welborn TA, Knuiman MW. Onset of NIDDM occurs at least 4–7 years before clinical diagnosis. Diabetes Care. 1992;15(7):815–819.