失效連結：修订间差异

一項於2003年發表的研究發現，在一星期內，平均每200條網上連結就會有1條成為失效連結<ref name=Fetterly2003>{{cite conference | first1 = Dennis | last1 = Fetterly | first2 = Mark | last2 = Manasse | first3 = Marc | last3 = Najork | first4 = Janet | last4 = Wiener | year = 2003 | title = A large-scale study of the evolution of web pages | url = http://www2003.org/cdrom/papers/refereed/p097/P97%20sources/p97-fetterly.html | access-date = 2010-09-14 | conference = | | | }}</ref>，[[半衰期]]為138週。

另一項於2004年發表的研究則顯示，某些網上連結（比如連接至某些檔案類型的連結、由學術機構託管的連結）的半衰期可能異於其他連結<ref name=Koehler2004>{{cite journal | first = Wallace | last = Koehler | year = 2004 | title = A longitudinal study of web pages continued: a consideration of document persistence | url = http://www.informationr.net/ir/9-2/paper174.html | journal = Information Research | volume = 9 | issue = 2 | access-date = 2019-01-31 | | | }}</ref>。與一般[[统一资源定位符|網址]]相比，在出版物中出現的網址需經過更長時間才會失效。Weblock在2015年的一項研究中，分析了三間[[开放获取]]出版社的文集，並從中提取180,000個線上參考來源。最終發現該些連結的半衰期約有14年<ref>{{cite web | title = All-Time Weblock Report | year = 2015 | url = https://weblock.io/report?id=all | access-date = 2016-01-12 | | | }}</ref>，這跟2005年的研究結果大致相符——它發現半數在《{{link-en|D-Lib杂志|D-Lib Magazine}}》中被引-{}-用的線上來源能夠在10年後繼續有效<ref name=McCown2005>{{cite conference | first1 = Frank | last1 = McCown | first2 = Sheffan | last2 = Chan | first3 = Michael L. | last3 = Nelson | first4 = Johan | last4 = Bollen | year = 2005 | title = The Availability and Persistence of Web References in D-Lib Magazine | url = http://www.iwaw.net/05/papers/iwaw05-mccown1.pdf | | access-date = 2005-10-12 | | }}</ref>。另有研究顯示，於學術文獻中引-{}-用的線上來源擁有較高的失效機會，不過半衰期則達4年以上<ref name=Spinellis2003>{{cite journal | first = Diomidis | last = Spinellis | year = 2003 | title = The Decay and Failures of Web References | url = http://www.spinellis.gr/pubs/jrnl/2003-CACM-URLcite/html/urlcite.html | journal = Communications of the ACM | volume = 46 | issue = 1 | pages = 71–77 | doi = 10.1145/602421.602422 | access-date = 2007-09-29 | | | }}</ref><ref name=Lawrence2001>{{Cite Q | Q21012586 }}</ref>。《{{link-en|BMC生物信息學|BMC Bioinformatics}}》於2013年刊登了一篇研究報告，當中以Web of Science的摘要為研究對-{}-象，分析當中近15,000條連結。結果發現該些網頁有50%在9.3年後繼續有效，整體只有約6成有線上存檔<ref>{{Cite journal | last1 = Hennessey | first1 = Jason | last2 = Xijin Ge | first2 = Steven | title = A Cross Disciplinary Study of Link Decay and the Effectiveness of Mitigation Techniques | journal = BMC Bioinformatics | volume = 14 | pages = S5 | date = 2013 | doi = 10.1186/1471-2105-14-S14-S5 | pmid = 24266891 | pmc = 3851533}}</ref>。

一項2002年的研究顯示，與其他連結相比，於數位圖書館上出現的連結需較長時間才會失效<ref name=Nelson2002>{{cite journal | first1 = Michael L. | last1 = Nelson | first2 = B. Danette | last2 = Allen | year = 2002 | title = Object Persistence and Availability in Digital Libraries | doi = 10.1045/january2002-nelson | journal = D-Lib Magazine | volume = 8 | issue = 1 | url = https://digitalcommons.odu.edu/cgi/viewcontent.cgi?article=1008&context=computerscience_fac_pubs | doi-access = free | access-date = 2019-09-24 | | | }}</ref>。

各種各樣的原因都會令超連結失效。網站的管理人決定把網站刪除便是一例。其他原因還有管理人把內容移動至新[[域名]]、網站所使用的技術過舊、沒有更新域名注册信息<ref>{{Cite book|title=Partners for Preservation: Advancing digital preservation through cross-community collaboration|last=Kramer-Smyth|first=Jeanne|publisher=Facet Publishing|year=2019|isbn=9781783303472|pages=70|url=https://books.google.com.hk/books?id=t0faDwAAQBAJ&pg=PA70#v=onepage&q&f=false|access-date=2021-06-17|||}}</ref>、伺服器停止運作<ref>{{Cite book|title=Good Research Practice in Non-Clinical Pharmacology and Biomedicine|editor-last1=Bespalov|editor-first1=A.|editor-last2=Michel|editor-first2=M. C|editor-last3=Steckler|editor-first3=T.|publisher=Springer Nature|year=2020|isbn=9783030336561|pages=284|url=https://books.google.com.hk/books?id=PPHRDwAAQBAJ&pg=PA284#v=onepage&q&f=false|access-date=2021-06-17|||}}</ref>。

防止連結失效的方法有盡可能使用沒太大可能失效的連結、以各種方式保護現有連結免於失效、修复因內容移動或刪除而失效的連結。當中最基本的方法就是創造出不會隨時間而改變的網址<ref name=Berners-Lee1998>{{cite web |author-link = Tim Berners-Lee |first = Tim |last = Berners-Lee |title = Cool URIs Don't Change |year = 1998 |url = https://www.w3.org/Provider/Style/URI |access-date = 2019-01-31 |||}}</ref>。

* 張貼簡潔網址<ref name=Kille2014>{{cite web | last = Kille | first = Leighton Walter | title = The Growing Problem of Internet "Link Rot" and Best Practices for Media and Online Publishers | publisher = Journalist's Resource, Harvard Kennedy School | date = 2014-11-08 | url = http://journalistsresource.org/studies/society/internet/website-linking-best-practices-media-online-publishers | access-date = 2015-01-16 | | | }}</ref>

* 張貼連接至[[互联网档案馆]]<ref>{{cite web | url=https://archive.org/ | title=Internet Archive: Digital Library of Free Books, Movies, Music & Wayback Machine | date=2001-03-10 | access-date=2013-10-07 || | }}</ref>、[[WebCite]]<ref name=Eysenbach2005>{{cite journal | first1 = Gunther | last1 = Eysenbach | first2 = Mathieu | last2 = Trudel | year = 2005 | title = Going, going, still there: Using the WebCite service to permanently archive cited web pages | doi = 10.2196/jmir.7.5.e60 | journal = Journal of Medical Internet Research | volume = 7 | issue = 5 | pages = e60 | pmid = 16403724 | pmc = 1550686}}</ref>、[[Archive.is]]、 Perma.cc<ref name=permacc>{{cite journal |last1 = Zittrain |first1 = Jonathan |last2 = Albert |first2 = Kendra |last3 = Lessig |first3 = Lawrence |url = https://cdn.harvardlawreview.org/wp-content/uploads/2014/03/forvol127_zittrain.pdf |title = Perma: Scoping and Addressing the Problem of Link and Reference Rot in Legal Citations |journal = Legal Information Management |volume = 14 |issue = 2 |pages = 88–99 |date = 2014-06-12 |doi = 10.1017/S1472669614000255 |access-date = 2020-06-10 |||}}</ref>、Amber<ref>{{Cite web|title = Harvard University's Berkman Center Releases Amber, a "Mutual Aid" Tool for Bloggers & Website Owners to Help Keep the Web Available {{!}} Berkman Center|url = https://cyber.law.harvard.edu/node/99276|website = cyber.law.harvard.edu|access-date = 2016-01-28|||}}</ref>等网络档案馆的連結