R. Chen et al., THE EFFICIENCY OF THE SETS AND THE CUSCORE TECHNIQUES UNDER BIASED BASE-LINE RATES, Statistics in medicine, 16(12), 1997, pp. 1401-1411
Statistical techniques used for surveillance of disease incidence rate
s are generally based on the assumption of known baseline rate of the
disease monitored, whereas actually it is an estimate obtained from a
large sample, As a result, the time interval until true or false alarm
is shorter or longer than assumed. In this study, we evaluate the per
formance of the sets and of the cuscore techniques when the estimate o
f the baseline rate is biased. We evaluate the effect of an underestim
ated baseline rate with respect to frequency of false alarms and to th
at of an over estimated rate with respect to the delay until elicitati
on of a true alarm. We evaluate the effects of 5 per cent and 10 per c
ent bias in the estimated baseline rate for specified conditions assoc
iated with sparse data The results show that the effect of plus or min
us 5 per cent bias in the estimate are moderate and those of 10 per ce
nt we substantial. In general, the effect of an overestimated baseline
rate is greater on the sets technique than it is on the cuscore techn
ique and the effect of an underestimated rate is greater on the cuscor
e technique than it is on the sets technique. However, the differences
between the two techniques are small on both perspectives. The two me
thods differ also with respect to the expected time until true alarm w
hen the specified baseline rate is unbiased. The sets technique is the
more efficient in detecting a two-fold increased rate when the number
of diagnoses expected annually (E(X)) is less than 1.62, and the cusc
ore is the more efficient technique when E(X) > 1.62. We use the term
'turning point' to define the regions in which the sets technique and
the cuscore techniques are preferred. With an estimated baseline rate
that is 5 per cent higher than the actual rate, the turning point fall
s from 1.62 to 1.45 when the rate is twice the baseline rate, and from
5.75 to 4.34 when the rate is triple the baseline rate. (C) 1997 by J
ohn Wiley & Sons, Ltd.