Defining the population under study is a critical component of all epidemiological studies. Like case definitions, the population under study must have characteristics which set its members apart from non-members. These members can then be categorized into smaller groups for the purposes of comparing disease levels between different sub-groups within the study population. Defining the population of interest in apiculture represents a unique challenge as there is a hierarchy of population units, each of which could be considered “individual members” (Table 1). In apicultural terms there are several levels of potential interest, thus there are several different definitions for what makes up the individual of interest.
- Individual bees within a colony
- A group of colonies located within one area make up an apiary
- One or more groups of apiaries owned or managed by one beekeeper make up an operation
- Apiaries contained within a defined geography make up a region
Characteristics that commonly define sub-groups within any of these given populations often differ according to hierarchal classification of the population, but broadly include individual attributes, such as: age (i.e. bee cohort at the colony level (Giray et al., 2000); genetics (i.e. patriline at the colony level (Estoup et al., 1994), queen type at the apiary level); size of operations; production objectives; and management style (at the regional level) (Table 1).
Once the defining criteria for a population have been established, the membership (epidemiological unit) of that population can be quantified. However, size may change over time because new members are added or existing members are removed.