Abductive validation is the process of validating a given hypothesis through abductive reasoning. Cross-validation is a statistical method for validating a predictive model. Advertisers use proxy servers for validating, checking and quality assurance of geotargeted ads. These types of studies are useful for validating suspected usability issues. Established engineering disciplines use mathematical analysis as the foundation of creating and validating product design. Mitigation strategies include adding consistency checks, validating inputs, and using specialized tools. Performing thermal testing can also help with validating the cold chain. Unbound is a validating, recursive and caching DNS server designed for high performance. The disadvantage is the difficulty in developing and validating the proper model. There are several main methods of validating PINs. In addition to using these functions, validating or sanitizing the user input is also recommended. Negative models essentially refer to control animals, which are useful for validating an experimental result. The Catholic Church says that it maintains particularly stringent requirements in validating the miracle's authenticity. Unbound is a validating, recursive, and caching DNS resolver product from NLnet Labs. Emulation is widely used in the design stage for validating communication networks prior to deployment.