text: Bioassay can be classified by how it is applied and how the response is recorded.
  ; Direct assay
  : In a direct assay, the stimulus applied to the subject is specific and directly measurable, and the response to that stimulus is recorded. The variable of interest is the specific stimulus required to produce a response of interest (ex. death of the subject).
  ;Indirect assay
  :In an indirect assay, the stimulus is fixed in advance and the response is measured in the subjects. The variable of interest in the experiment is the response to a fixed stimulus of interest.
  ;Quantitative response
  :The measurement of the response to the stimulus is on a continuous scale (ex. blood sugar content, degree of color change in cell growth medium).
  ;Quantal response
  :The response is binary; it is a determination of whether or not an event occurs (ex. death of the subject).