Why Is a Lifetime Metric Value Less for the Current Day Than the Previous Day?

Question

Why is a lifetime metric value less for the current day than the previous day?

Answer

In Facebook Pages, lifetime metrics are usually n > n-1, where n is yesterday's date. In some cases though, the value returned from the Facebook API for the lifetime metric is less than the value for the previous date.

We have seen this occur repeatedly. Facebook's documentation does not clearly outline this occurrence or potential reasons for it.