The age and gender demographics roughly matched those of the four risk score derivation cohorts; co-morbidities such as hypertension and hyperlipidemia were of comparable prevalence to the GRACE derivation cohorts, but more prevalent than in the TIMI derivation cohorts (Table S1).
When applying such weighted Cox models in the initial risk model derivation, we found similar slight bias.
Combined with baseline risks, corresponding effect estimates could be derived for the three other risk formats (derivations not shown, but available upon request).
The order of risk groups derived from the derivation set was maintained in the internal and external validation.
The first served to develop the risk assessment instrument (derivation sample).
Approximately 67%% of persons with APN were classified as high risk in the derivation subgroup and the c-statistic was 0.81, indicating good to excellent discrimination [ 6].
An HI > 1 may prompt a risk assessor toward derivation of tissue- and mechanism-specific HIs to more accurately evaluate the mixture (U.S. EPA 1989b), although assessors are not required to do so.
Overall 5,322 variables were derived, but only those that appeared more than 4 times among the patients at risk in the derivation cohort were kept, resulting in 202 variables.
Reassurance that such a strategy would be appropriate comes from our mortality data, indicating an approximate 1% excess all-cause mortality (compared with actuarial data) in the low risk groups of derivation and validation cohorts.
Most scoring systems use clinical vital signs such as heart rate, respiratory rate, blood pressure, temperature and pulse oximetry for risk stratification model derivation [ 13], but these physiological measures might not correlate well with short- or long-term clinical outcomes [ 14, 15].
