Why is it that sometimes the estimate for a group is suppressed while the estimate of a smaller subgroup is not suppressed?

When addressing suppression, sample size, variance, and design effects are all considered. Sometimes, that means that estimates for larger groups are suppressed while estimates for smaller groups are available.

The Statistical Inference Report outlines procedures for when suppression is applied. Chapter 9 explains these procedures, and they are summarized in Table 9.1. Sample codes for identifying unreliable output in SUDAAN®, Stata®, SAS®, R, and SPSS® are available in Appendix A. A shorter explanation is also available in the annual Methodological Summary and Definitions (MSD), chapter 3.2.