Figure 1.

Stepped wedge design: schematic of the phased implementation of Chlamydia Screening Implementation in three blocks (A,B, and C). The design enables comparison of prescreening (A1 and B1) and post-screening prevalences after the first round (A2 and B2) and after the second round (A3)

van den Broek et al. BMC Infectious Diseases 2010 10:89   doi:10.1186/1471-2334-10-89
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