A bioassay or biological assay is a biological testing procedure for estimating the concentration of a pharmaceutically active substance in a formulated product or bulk material. In contrast to common physical or chemical methods, a bioassay results in detailed information on the biological activity of a substance. Over the last decade bioassays and biostatistical analysis have become more important in effectively controlling the quality of biopharmaceutical development and manufacturing. Biological assays are typically performed in vivo or in vitro. In vivo bioassays investigate effects of a substance on a living organism, for example, injecting insulin in rabbits to measure the blood glucose level. In vitro bioassays allow a controlled environment outside the usual biological context. Typical examples are binding assays (for example ELISA), enzyme activity assays (for example spectrophotometric, fluorometric or radiometric assay), cell based assays (e.g., cell proliferation, cytotoxicity, or cell death assay) or cell and gene therapy assays.