Universal Principles of Design, Updated and Expanded Third Edition

080 Garbage In – Garbage Out

The quality of system output is largely dependent on the quality of system input.

The garbage in–garbage out principle is based on the observation that good inputs generally result in good outputs, and bad inputs, barring design intervention, generally result in bad outputs. The rule has been generalized over time to apply to all systems and is commonly invoked in domains such as business, education, nutrition, and engineering.1

The garbage-in metaphor refers to one of two kinds of input problems:

• Problems of type — Occur when the incorrect type of input is fed into a system, such as entering a phone number into a credit card number field. Problems of type are serious because the input provided could be radically ...