059 Garbage In-Garbage Out

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

• The “garbage in” metaphor refers to two categories of input problems: type and quality.

• Problems of type occur when the wrong type of input is provided; for example, entering a phone number into a credit card number field.

• Problems of quality occur when the correct type of input is provided, but with defects; for example, entering a phone number into a phone number field, but entering it incorrectly.

• Avoid garbage-out by preventing garbage-in. Use affordances and constraints to minimize problems of type. Use previews and confirmations to minimize problems of quality.

See Also Affordance • Confirmation • Constraint • Errors Feedback Loop • Signal-to-Noise Ratio

The Mars Climate Orbiter disintegrated in the Martian atmosphere in 1999. The cause? Garbage in-garbage out. Trajectory corrections were entered in English units versus the required metric units, dooming the craft.