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Oral Health, U.S. 2002 Annual Report
Section F: TECHNICAL NOTES
Analytic Methods

Oral Health U.S., 2002 contains predominantly descriptive statistics including frequencies, percentages, ratios, incidence, prevalence and mortality rates, and calculations of cost. In general, only results with statistical significance at the 95% confidence level are discussed unless otherwise stated. SAS, versions 6.12 and 8.0 (SAS, 1999), and SUDAAN, versions 7.5.3A and 7.6 (Shah et al., 1997), were used for statistical programming with the exception of data from SEER (NCI, 2000). SEER data are provided with a self-contained statistical programming package that was used for analysis of these data (NCI, 2000).

Occasionally, data from published material were used. In these cases references are provided and statistical analytic methods vary with the source of data. Whenever possible, nationally representative data were used. The national surveys collecting these data generally use multistage probability samples. Resulting analyses employ sampling weights. In these instances SUDAAN was used to obtain accurate variances and confidence intervals. Confidence intervals are provided in tables whenever possible. In some cases, data were obtained from published documents and confidence intervals were not available. The significance of trends was examined by performing a regression analysis on the data (Korn & Graubard, 1999). The most recent data available for each indicator were used. In a few cases an indicator was considered important enough to include even though the most recent data were more than 5 years old. Some data are reported for which the numbers are too low for statistical evaluation. This was done when these data were the only source available.

Differences between population subgroups were examined using demographic variables. These variables include age, gender, race/ethnicity, education, and federal poverty level. The age groups used for analysis vary depending on the medical/health implications of the indicator. In some cases age groups vary depending on how data in individual surveys were collected. Education is presented with three categories: less than 12th grade or 12 years of education, 12th grade or 12 years of education, and more than 12th grade or 12 years of education. For adults, the education of the survey participant is used. For children and adolescents, the education of the person identified as head of household is used. The categorization of race/ethnicity depends on the individual survey. For instance, in NHANES III, Mexican Americans were oversampled and race/ethnicity is categorized as non-Hispanic white, non-Hispanic black, and Mexican American. In many analyses the numbers available for other racial/ethnic groups do not allow statistical conclusions to be drawn. In NHANES I, the groups of white, black, and other are most frequently used. Data from the NHIS generally use race/ethnic groups of non-Hispanic white, non-Hispanic black, and Hispanic. Other surveys may use white, black, and other or in some cases group white and other ethnic groups and consider black, or black and Hispanic as separate groups. Analyses are generally limited to the race/ethnic groups provided on public use tapes or CD-ROMs of survey data.

Federal poverty level is determined by income thresholds that vary by family size and the number of related children in the household who are younger than 18 years. Poverty thresholds are derived from the measure of poverty used for calculating the number of persons living in poverty in the United States or in states or regions. The thresholds do not vary geographically, but they are updated annually using the Consumer Price Index. See the Census Bureau's website (http://www.census.gov/ hhes/poverty/threshld.html) for more information. Different indicators of poverty status have been used by different federal agencies in the surveys they conduct. In most national surveys a poverty income ratio is presented. The poverty income ratio is the ratio of a family's income to the poverty threshold defined by the U.S. Census Bureau appropriate to the family's composition. For most analyses in this report, a cut point of 1.00 was used to differentiate those living below the federal poverty level (less than 1.00) from those living at or above the federal poverty level (1.00 or more). This cut point is used in NHANES I and III and in the NHIS. MEPS defines less than 100% of the federal poverty level as negative or poor; 100% to less than 125% as near poor; 125% to less than 200% as low income; 200% to 400% as middle income; and 400% and above as high income. BRFSS reports only income categories with no associated poverty level categories.

The issue of separating the effects of race/ethnicity and income was approached by stratifying the sample on one variable and looking at the second variable within each stratum. For instance, comparisons between racial/ethnic groups were done separately for those living below the poverty level and for those living at or above it. These analyses are limited by the sample sizes in each group.

If data suggested an age dependency or if various subgroups being compared included individuals with large differences in age distribution, analyses were age adjusted to evaluate the possible impact of different age distributions on the observed results. Procedures based on those described by Anderson and Rosenburg (1998) were used. Direct age standardization applies age-specific rates from two or more sample populations to a standard age distribution in order to eliminate differences in the observed rates that are due to differences in age distributions between populations. This weighted average of the category-specific rates provides a single rate that reflects the numbers of events that would have been expected if the populations being compared had identical age distributions (Hennekens & Buring, 1987). Age adjustments in this report were made using the year 2000 U.S. population age distribution (Anderson & Rosenburg, 1998), with the exception of data from SEER. In this case the statistical analysis program provided calculates age adjustment to the 1970 U.S. population.

REFERENCES
Anderson RN, Rosenburg HM. Age standardization of death rates: implementation of the year 2000 standard. National Vital Statistics Reports; vol. 47 no. 3. Hyattsville, MD: National Center for Health Statistics, 1998.

Hennekens CH, Buring JE. Epidemiology in Medicine. Boston: Little, Brown and Company, 1987. Korn EL, Graubard BI. Analysis of Health Surveys. New York: Wiley, 1999.

National Cancer Institute. SEER Cancer Incidence Public-Use Database CD-ROM, 19731997. Bethesda, MD: U.S. Department of Health and Human Services, Public Health Service, 2000.

SAS Institute Inc. SAS/STAT User's Guide, Version 8. Cary, NC: SAS Institute, Inc., 1999.

Shah BV, Barnwell BG, Bieler GS. SUDAAN User's Manual, Release 7.5. Research Triangle Park, NC: Research Triangle Institute, 1997.


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