# 1.3.3.1 Total colony loss (TL) (the cumulative incidence of mortality)

This is the percentage of colonies lost in a specific group over a fixed period of time. This figure is the most accurate snap shot of loss in a defined group, such as in an operation or geographic region. If all colonies in a region were enumerated it would give a precise figure for the proportion of all colonies that died in that region. However, within the population of interest, operations with large numbers of colonies will have a greater influence on the total colony loss metric than will the operations with only few colonies. Total Colony Loss in an operation or in a defined group is calculated by dividing the total number of colonies that died over a given time period (T_{dead}) by the total number of colonies at risk of dying in a given time period (T_{Colonies }_{at risk}) and multiplying the quotient by 100% (Equation 1.3.3.1).

Where the total number of colonies at risk of dying (T_{Colonies }_{at risk of}_{ }_{dying}) over a period was calculated by adding the number of colonies at the start of the period (T_{Start}) with the number of splits made by the beekeepers over the period (T_{Splits}) and the number of colonies purchased over the period (T_{Purchased}) and then subtracting the number of colonies removed (sold or given away) over the period (T_{Removed}).* *

And where the total number of colonies that died (T_{Dead}) was calculated by subtracting the total number of colonies at the end of a period (T_{End}) from the total number of colonies at risk of dying for the ^{period}^{ }^{(T}colonies at risk of dying^{).}* *

Where period was the defined period of time for which colony loss was analysed. The unit of time, is the period defined by the time between T_{Start }and T_{End}. This unit is often not reported and is often loosely defined by the season encompassed by that time period (e.g. winter).

And where, respondents in a specific group are the group of respondents for whom valid loss data was collected.

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