Figures one and two were unclear in, FJT Burke, V Singh, and NHF Wilson (2013) The Normalized Failure Index: A Method for Summarizing the Results of Studies on Restoration Longevity?. Operative Dentistry: September/October 2013, Vol. 38, No. 5, pp. 488–496. They have been recreated below. You have our apologies for any confusion they might have caused.
