In the past decade an average of almost 400 events each year have met the U.N.criteria for a natural disaster.

VOA: standard.2009.10.14

If you have a sample with n observations, it's the summation I = 1 to n of xi/n--that's the average.

如果你有n个观测值,对Xi从i=1到n求和再除以n

耶鲁公开课 - 金融市场课程节选

They found N-BNP levels were on average three times higher in patients who died during the period of the study than in those who survived.

BBC: Test to predict heart attack survival

Even though big-box centers across the U.S. still are struggling with vacancies lingering from the liquidation of retailers such as Borders, Circuit City and Linens N' Things, the industry's average vacancy rate has declined in recent years.

WSJ: Landlords Prefer Deals LIke Office Depot-OfficeMax to Liquidations