ABSTRACT
It is essential to distinguish between responses produced by a test compound and the changes which occur in plasma and urine as normal biological variations, particularly where statistical differences are found for data in the absence of any other findings. For each study, we can consider several variables or experimental steps: these variables can be divided into (1) biological, (2) analytical and (3) pharmacological or physiological effects due to the test compound: these three components may interact in a synergistic or antagonistic manner. Sometimes these variables are expressed as: 1 Biological variance
The methodological variance is introduced by the experimental procedures during the study. This variable is important when data are compared for the same test compound where the route of administration may differ or the study is repeated in another centre using slightly different experimental procedures.
