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Table 2 The follow-up rate at each annual interval after subjects (N = 610) in a retrospective cohort study of 3-year and 5-year prostate cancer (PrCa) recurrence risk based on electronic medical record (EMR) data

From: New methods for estimating follow-up rates in cohort studies

Follow-upb Nc Percentage Method
η percentage
Estimated follow-up using the formal method η FPT Clark’s completeness index
Simplified Person-time Method
1 Year 558 91.4% 95.7% 95.5% 95.7%
2 Year 472 86.2% 95.0% 94.5% 95.0%
3 Year 383 80.9% 93.6% 92.9% 93.8%
4 Year 295 75.6% 92.5% 92.3% 93.3%
5 Year 197 67.5% 91.8% 91.8% 93.0%
  1. Follow-up rates were estimated using four methods, namely, (i) the standard Percentage Method (Eq. 1 a), (ii) the formal Method (FPT, Eq. 4), (iii) the Clark’s completeness index (CCI, Eq. 2), and (iv) the Simplified Person-Time Method (SPT, Eq. 5)
  2. aEquations are shown in the next
  3. bA retrospective cohort study was conducted among incident PrCa patients who underwent robotic assisted laparoscopic prostatectomy (RALP) by a single surgeon at Montefiore Medical Center (MMC) in the Bronx from 10/2005 through 12/2012. These subjects were followed for disease recurrence or progression through December 2012. A total of N = 610 PrCa patients who underwent RALP and had their follow-up at MMC were included in this analysis
  4. cWe calculated the follow-up rate at each year among the subset of the patients who had RALP early enough to be eligible for such length of follow-up. For example, to estimate the three year follow-up rate, we calculated this rate among the subjects who had RALP at least before 12/31/2009