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Table 2 Sample Size calculation prognostic value, internal validation [38, 39]

From: A risk assessment model for chronic ankle instability: indications for early surgical treatment? An observational prospective cohort – study protocol

EPV = no. of events/no. of regression coefficients
Minimal EPV ≥10 Prognostic Value ≥20 Prediction Model
Change of developing CAI 30–40% 30–40%
No. of regression coefficients 16 16
(? = no of events needed) 10 =?/16
? = 160
minimal 160 events
20 =?/16
? = 320
→ minimal 320 events
In case of 30% chance of developing CAI 160*3.33 = 532.8 patients 320*3.33 = 1065.6 patients
In case of 40% chance of developing CAI 160*2.5 = 400 patients 320*2.5 = 800 patients
Sample Size (incl. 10% loss to follow-up) 445–593 patients 889–1185 patients