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Cumulative uptake of the test for fecal occult blood (gFOBT) during the whole observation period, taking into account the renewed randomization of the study population with mailing of invitations after the end of year 1. Because of the almost identical pattern of utilization within the first 12 months without enclosure of a test kit, the groups “Only year 1” and “No letter year 1” were amalgamated.
