garbage in, garbage out incorrect or poor quality input inevitably produces faulty output.

☞ This expression is often abbreviated as GIGO. The phrase originated in the mid 20th century in the field of computing, but it can now have a more general application.

2013CNN Transcripts My main message was that this is one of the most poorly conducted investigations I had ever seen outside of a third world country. It was frightenly bad. And of course, you know, garbage in, garbage out.