Design of experiments using the microcytotoxicity assay.

Examination of data from the microcytotoxicity assay revealed that the number of surviving target cells varies systematically both between microtest plates and within plates. If the layout of treatments on the plate is not planned carefully, these effects decreased precision and introduce bias. It is recommended that treatments which are to be compared be placed close together on the plate; for example, a plate with 96 wells might be considered as 24 blocks of 4 wells, with the treatments placed within these blocks. Data can be analyzed by means of paired t-tests or randomized block analysis of variance. These design changes remove the effect of systematic variation and increase the precision of the assay.