where exp is the base of the natural logarithm raised to the
quantity within the brackets and A, B, C, and D represent the numerical entries in
the summary format in Table 8–6, and VAR(lnRR) is the estimated variance of the
natural logarithm of the RR. This confidence
interval is approximate because it is based on a computational short-cut
for estimating the variance of the natural logarithm of the RR. For relatively large samples, this
approximation yields confidence limits that are quite close to the
exact values, which are much more difficult to calculate.