Some psychological evidence on how people debug computer programs

Abstract

Ten experienced programmers were each given the same 12 FORTRAN listings to debug. Each listing contained a non-syntactic error in one line. Median debug times (7 min), number of bugs not found (11% of the listings), and number of incorrect assertions about the location of the bug (less than one per listing) all replicated earlier results (Gould & Drongowski, 1974). Although subjects were given the opportunity to use the interactive debugging facilities of an on-line computer, they rarely did so. Bugs in assignment statements were about three times as hard to detect as array or interaction bugs. Debugging was about three times as efficient on programs subjects had debugged previously (although with a different bug). A number of basic concepts relating to debugging are identified and a gross theory of debugging is described. © 1975, Academic Press Inc. (London) Ltd.. All rights reserved.