# Power calculation for a test of trend over time

This paper (open access) Babies born at the threshold of viability: changes in survival and workload over 20 years (table 2) presents data for survival of extremely premature babies over the last 20 years in 4-year time periods. They state that the survival of 23-week gestation babies has not improved over this time (p=0.08). Does this test of trend have sufficient power to detect a trend if one existed? How could I determine that?

You have misinterpreted the results of the statistical test just as the authors of that paper somewhat misinterpreted it in the conclusion section of their paper. It is concerning that we continue to quote $P$-values without effect estimates and confidence limits (which also lessen the need to talk about power). The problem is well summarized in the classic paper Absence of Evidence is not Evidence of Absence.