A complementary analysis is a planned analysis that supports a primary analysis by providing evidence relevant to counterclaims that might be raised concerning the primary analysis. A complementary analysis sheds light on counterclaims. A compelling observational study is often composed of a strong primary analysis protected by a bodyguard of strong complementary analyses. When the primary analysis is based on a block design, a complementary analysis may be based on tightened blocks—that is, a smaller block design formed by either removing some controls from a block or some entire blocks or both, in an effort to address particular counterclaims.