A wide range of scales and indices are used to describe natural hazards and their impacts. Some scales infer damage levels from hazard characteristics while others use damage levels to estimate a physical characteristic. Damage scales may rely on raw dollar values, percent loss estimates, damage states, normalized values or macrodamage categories. Whatever the basis of the scale it should tell the truth. However, scales are compromises between the need for detailed information and being simple enough to use. Damage scales may be nominal (categorical), ordinal, interval or ratio scales. Frequency words such as "few", "many" can be dealt with in a range of ways to produce contiguous, widely separated, broadly overlapping or narrow overlapping values. Most scales rely on maximum values but some focus on minimum or threshold values. The number of levels on damage scales commonly ranges from five to 13. Some long-lived damage scales have evolved through several editions, changing to reflect the new or additional uses to which they have been put and as buildings and the nature of damage to those structures has changed. Few scales state precisely the purpose of the scale, deal clearly with ambiguities or provide guidelines for the use of qualitative information.
