A simple method to adjust clinical prediction models to local circumstances

Table 1 Distribution of the characteristics of patients who underwent surgery in the Amsterdam cohort between April 1997 and January 1999 and patients who underwent surgery in the Utrecht cohort between February and December 2004; % (n) unless stated otherwise

Patient characteristics	Amsterdam cohort 1997–1999 (n = 1944)	Utrecht cohort 2004 (n = 1035)
Female gender	57 (1110)	58 (596)
Age (years)^a	43 (15)	47 (16)
Preoperative pain score (NRS)^a	3.0 (2.7)	3.4 (2.9)
Type of surgery
Lowest expected incidence of pain	4 (72)	9 (92)
Low expected incidence of pain	30 (590)	29 (297)
Medium expected incidence of pain	18 (348)	19 (200)
High expected incidence of pain	35 (671)	33 (339)
Highest expected incidence of pain	14 (263)	10 (107)
Ambulatory surgery	28 (549)	43 (444)
Expected incision size ≥10 cm	37 (724)	7 (67)
APAIS anxiety score^a	9.4 (4.0)	9.5 (3.9)
APAIS need for information^a	6.5 (2.2)	6.2 (2.3)
Severe acute postoperative pain, NRS ≥ 6	62 (1205)	36 (374)

NRS numeric rating scale; APAIS Amsterdam preoperative anxiety and information scale. Reprinted with permission from Janssen et al.32
^aMean (standard deviation)