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Assessment of self-selection bias. SSB self-selection bias; Sstu, Spop: self-reported Syphilis diagnoses in the last 12 months in the study (stu)/Syphilis cases attributed to MSM in the primary surveillance data (pop); Nstu, Npop: Number of MSM in the study (stu)/in the German population (pop), the latter based on extrapolations from sexual behaviour surveys of the general population.
