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Cumulative probability of major abdominal surgery stratified by time period of diagnosis. Using the period 1970–74 as a reference, there was no significant association between time to first major abdominal surgery with calendar period: 1970–74 versus 1975–79 (p=0.78), 1980–84 (p=0.97), 1985–89 (p=0.52), 1990–94 (p=0.81), 1995–99 (p=0.22), and 2000–04 (p=0.22).
