4.9 Statistics Applied to Biological Assays

Biological assays are those carried out by dosing a biological test system (such as a rat or mouse) with the substance to be determined, and measuring a response. An example is the USP monograph for Menotropins. This biological extract contains Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH), which have effects on the reproductive organs. The assay consists of dosing male (LH) and female (FSH) rats with menotropins and observing the effects (weight) on the seminal vesicles and ovaries respectively after a multiple day incubation time.

Although this type of assay will rarely be encountered in the ORA laboratory, biological assays are instructive in the statistical complexity encountered when dealing with highly variable systems such as live animals. The interpretation of results is complicated by the fact that the total variance of a measurement includes a large variance due to the biological component. The analyst may also encounter these assays when on team inspections.

The subject of biological assays is addressed in General Chapter <111> of the USP, "Design and Analysis of Biological Assays," where an extensive statistical treatment is developed, based on the Analysis of Variance (ANOVA). This is also one of the rare instances in the USP where rejection of "outlier data" is allowed, under strict statistical justification. The interested reader is referred to <111> for further information.