Difference between setting a spike period to a rolling week versus a calendar week
There is a difference in behavior when a spike period is set to a rolling week versus when it is set to a calendar week. When using rolling time, the periods will be completely full and span the entire week.
When deciding whether to use a calender week or rolling week for the spike value, keep these guidelines in mind.
Use a rolling time period when you want to compare a complete period ending at the point of the transaction.
Use calendar periods when you want to compare a period that is in the process of completion, to a fixed historical period.
A calendar comparison is more appropriate for uncovering abrupt changes; whereas a rolling comparison is more appropriate for changes that are smoothed into even divisions.
In the example above, the spike period was set to one rolling week. In that case, the week of the spike period is a full seven days long, ending at the current time. The spike value returned from that seven day period will be compared to the average of the twelve other rolling weeks which begin and end at the same time and day of the current transaction.
If a calendar week were used in the previous example, there would only be data in the current calendar week between the beginning of that week and the current transaction time (which would generally be a fraction of a week). The spike value returned from that calendar week period would be compared to the average of the twelve other calendar weeks which begin and end on strict calendar week boundaries.
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