Improving maintainability is generally easier than improving reliability. There were also problems with early ammunition reliability and accuracy. The rifle has extreme reliability and durability under all conditions. The model exceeded operational maintenance, reliability, and availability specifications. The M9 had the lowest levels of soldier confidence in reliability and durability. There may be performance or reliability considerations. The modifications increased both reliability and validity. Internal reliability and concurrent validity are acceptable. The scale has high reliability and validity. Both reliability and validity can be assessed statistically. This has come at the cost of reliability and maintainability. It broke records for tactical aircraft in availability, reliability, and maintainability. Psychometricians generally regard IQ tests as having high statistical reliability. Approaches to reliability and validity vary, however. The term reliability, availability and serviceability (RAS) is a defining characteristic of mainframe computers.