The sample design for NHANES makes it possible to combine two or more survey cycles to increase the sample size and analytic options. Each 2-year cycle and any combination of 2-year cycles is a nationally representative sample. However, sometimes the size of a particular sample is too small in an individual 2-year cycle to produce statistically reliable estimates. Fortunately, the NHANES sample design makes it possible to combine two or more cycles to increase the sample size and analytic options.