  Wikipedia, the Web's largest encyclopedia, frequently faces content disputes
or malicious users seeking to subvert its integrity. Administrators can
mitigate such disruptions by enforcing "page protection" that selectively
limits contributions to specific articles to help prevent the degradation of
content. However, this practice contradicts one of Wikipedia's fundamental
principles$-$that it is open to all contributors$-$and may hinder further
improvement of the encyclopedia. In this paper, we examine the effect of page
protection on article quality to better understand whether and when page
protections are warranted. Using decade-long data on page protections from the
English Wikipedia, we conduct a quasi-experimental study analyzing pages that
received "requests for page protection"$-$written appeals submitted by
Wikipedia editors to administrators to impose page protections. We match pages
that indeed received page protection with similar pages that did not and
quantify the causal effect of the interventions on a well-established measure
of article quality. Our findings indicate that the effect of page protection on
article quality depends on the characteristics of the page prior to the
intervention: high-quality articles are affected positively as opposed to
low-quality articles that are impacted negatively. Subsequent analysis suggests
that high-quality articles degrade when left unprotected, whereas low-quality
articles improve. Overall, with our study, we outline page protections on
Wikipedia and inform best practices on whether and when to protect an article.
