Is it possible to combine WWEIA data from different release cycles?
Yes, the sample design for NHANES makes it possible to combine data cycles in order to increase the sample size and analytic options. However, in order to combine cycles appropriately, researchers must pay attention to variations between data cycles, including the following: • Sample weights – As a general rule, consult the version(s) of the NHANES analytic guidelines that correspond to the data cycles in question. To combine data from different cycles, it is necessary to use the same type of sampling weight from both cycles. For example, when combining dietary data from WWEIA 2003-2004 with WWEIA 2001-2002, use the special dietary intake data weights from both cycles and follow the specific instructions given in the analytic guidelines (e.g., on p. 12 of the Sept. 2006 revision of the Dec. 2005 update). Dietary intake data weights for 2001-2002 are slated for release in late 2006. Researchers wishing to analyze data before those weights are released will have to use the 2-year MEC wei
