Introduction
Overage is an important tool in the clinical supply planner's toolkit. It is used for various purposes; one of the most common is to account for enrollment uncertainty within a region. Some overage is often added to account for the risk of damaged goods, or other incidental waste or loss. Generally, we see companies using overage rates between 10 and 40%, though of course this is highly dependent on the cost of the study drug.
In Bluefin, depot demand is calculated by multiplying the percentage directly against the depot's aggregate site demand. The site demand takes into account site buffers, site shipment bundling, and lead times. If a central depot supplies a regional depot, no additional overage will be applied to demand from the central to the regional.
💡 Things to Note
We don't recommend using Overage in Bluefin to account for Site Seeding or Site Buffer Stock. Instead, use Supply Plans to take this into account.
Overage is an additional buffer beyond what Depot Buffers already provides. We recommend using Depot Buffers where more appropriate.
Be careful not to increase the Overage percentage intending it to function as a safety stock and use buffer stocks at site or depot levels; this will inflate the demand forecast beyond what is desired.
Setting Overage
Navigate to the Distribution tab on a scenario.
Expand the Overage section.
Set overage for all parts in a depot, or for an individual Depot-Part combination.
Example: Configuring Overage with a Central and Regional Depots
In a study with a central and regional depots, it is ok to set an overage percentage at both depots. Bluefin will not double-count site demand.
For example, in a study with a North America depot serving both North America sites and an EU regional depot, where we want to set 20% overage for the entire study, the following is correct.
Viewing Overage Results
Preview
Here, you can see the output of a depot demand preview with no overage.
After adding a 30% overage, we see our expected 13 units in the preview.
Reporting
Under Reporting, we have a "Depot Demand by Part" report that takes into account overage. By default, it will just show all depot demand going down the screen.
Bluefin tracks how much of the depot demand is because of overage. You can add the "Depot Demand Reason" column to "Column Labels" to get a pivot table comparing how much of the demand is from site demand directly, or from depot overage.
How Overage is Calculated in Bluefin
Depot demand in Bluefin follows the formula:
Depot Demand = buffered(Site Demand x (1 + Overage %))
Thus, overage is applied based on site demand, prior to any depot buffer calculations.
By setting overage for a depot or depot-part, all patient demand at sites served directly by that depot is taken into account. The overage quantity is then held at that depot, awaiting any demand that may occur.
How Overage is Distributed
Overage is rounded up and then distributed out over time to ensure accuracy. For example, in a study with 20 units total drug requested and 13% overage, the number of total units requested will be:
round(20 * .13) = round(2.6) = 3
Those three units will then be distributed out evenly over time. If you take the cumulative total demand at any given time, the amount of overage added to the demand should be equal to:
round(current_cumulative_units * overage_percentage)
In our 13% overage example, after 10 units of site demand, expect 1 unit of overage to have been added. After 15 units, expect 2 units of overage.