Although the intervention programs lasted 18 months, the protocol specified, primary outcome assessment occurred at 6 months because national guidelines recommend that individuals with persistent BP of 140/90mm Hg or higher after a period of lifestyle modification be referred for medication treatment.
During the design of the trial, we anticipated that approximately 30% of participants would have stage 1 hypertension at baseline.
Hence, we expected that a large number of individuals would need to be referred for medication treatment at 6 months, requiring censoring of their BP data, and that medication treatment would occur differentially across the 3 randomized groups. Defining the primary outcome at 6 months reduced the risk of bias and ensured that we would have a maximum number of BP measurements for analysis.