An experiment on the usefulness of design patterns: detailed description and evaluation

Advocates of software design patterns claim that using design patterns
improves communication between software people.
The controlled experiment that we describe in this report tests the
hypotheses that software maintainers of well-structured,
well-documented software containing design patterns can make changes
(1) faster and (2) with less errors
if the use of patterns is explicitly documented in the software.

The experiment was performed with 74 participants of a university
course on Java and design patterns.
It finds that both hypotheses appear to be true,
although the observed effects were relatively weak, presumably because
the tasks were too simple in the experiment.