  The verifiability of online information is important, but difficult to assess
systematically. We examine verifiability in the case of Wikipedia, one of the
world's largest and most consulted online information sources. We extend prior
work about quality of Wikipedia articles, knowledge production, and sources to
consider the quality of Wikipedia references. We propose a multidimensional
measure of verifiability that takes into account technical accuracy and
practical accessibility of sources. We calculate article verifiability scores
for a sample of 5,000 articles and 295,800 citations, and compare differently
weighted models to illustrate effects of emphasizing particular elements of
verifiability over others. We find that, while the quality of references in the
overall sample is reasonably high, verifiability varies significantly by
article, particularly when emphasizing the use of standard digital identifiers
and taking into account the practical availability of referenced sources. We
discuss the implications of these findings for measuring verifiability in
online information more generally.
