Using the National Death Index to validate the noninformative censoring assumption of survival estimation.
BACKGROUND
In survival analysis, a patient who is missing complete follow-up is included in the analysis as a censored observation. The analysis makes the assumption that the censoring is noninformative; that is, that a censored patient has the same risk of death as those who have complete follow-up. We tested this assumption in a large, long-term follow-up study.


METHODS
From 1986 through 2003, 14,495 patients underwent isolated coronary artery bypass grafting procedures. Of 13,963 eligible patients, 2312 were lost to follow-up. We obtained National Death Index data to complete our follow-up, and then compared survival between the original data and the complete National Death Index-augmented data.


RESULTS
The National Death Index data revealed 855 additional deaths and increased the total follow-up years from 86,810 to 102,157. Survival estimates and regression models did not differ between the original and National Death Index-augmented data.


CONCLUSIONS
Patients lost to follow-up might not differ with regard to survival from those with complete data. The requirement for 95% completeness is somewhat arbitrary. The quality and type of follow-up is more important than the percentage in time-related analyses.
Wu
YingXing
Y
Medical Data Research Center, Providence Health System, Portland, Oregon, USA. yingxing.wu@providence.org
Furnary
Anthony P
AP
Grunkemeier
Gary L
GL
D000368:Aged; D002423:Cause of Death; D015331:Cohort Studies; D003266:Continuity of Patient Care / Q000592:standards / Q000639:trends; D001026:Coronary Artery Bypass / Q000379:methods / Q000401:mortality*; D003327:Coronary Disease / Q000401:mortality* / Q000601:surgery*; D018572:Disease-Free Survival; D005260:Female; D005500:Follow-Up Studies; D017052:Hospital Mortality / Q000639:trends; D006801:Humans; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000401:mortality*; D011237:Predictive Value of Tests; D011336:Probability; D012042:Registries; D015203:Reproducibility of Results; D012189:Retrospective Studies; D018570:Risk Assessment; D012680:Sensitivity and Specificity; D016019:Survival Analysis