Standardized testing. To facilitate comparison of results across studies and particle types, standardized assays and response endpoints are needed. Standardized assays and tiered testing approaches have been recommended (Oberdorster et al., 2005b; OECD, 2008, 2010b), yet a relatively small number of the toxicology studies of nanomaterials provide sufficient data for risk assessment, and only a very few studies provide comparable dose–response data that can be evaluated across studies and particle types (NIOSH, 2010c).