2. Study design
Epidemiologists endeavour to reduce disease occurrence in a population. To achieve this one must quantify disease at the population level and determine risk factors that contribute to disease occurrence. Two study designs can be used to determine the association of exposure with a health outcome: observational and experimental. In an experimental design, the exposure is determined by the investigator, whereas in an observational design, the exposure is not determined by the investigator or the study (i.e. exposure is under the control of the study participants or the participant’s environment). For example, if an investigator determines which hives are treated for Nosema and which are not, then the study design would be considered an experimental design. In an observational study, the investigator would observe the Nosema responses for beekeepers who applied and who did not apply treatment for Nosema, wherein this case, the application of the treatment is determined by the beekeeper.