Except for the first and last observations, the average, sum, and end-of-period aggregation methods ignore any other missing values. For example, consider a daily series from 2003-06-01 to 2003-07-31 with a missing value for Friday 2000-07-04, the US Independence Day holiday. When converting from daily to weekly (Friday) values, for example, the week containing 2000-07-04 will be calculated using 4 values not 5. The end-of-period aggregation method will use the value for Thursday, 07-03, since the 07-04 value is missing. If Thursday and Friday both had missing values, the end-of-period aggregation method would use the value from Wednesday.