CONFIDENCE-INTERVALS FOR THE RELATIVE FREQUENCY OF RESPONDING CELLS IN LIMITING DILUTION ASSAYS

Confidence intervals for the relative frequency of responding cells in limiting dilution assays (LDAs) have not been examined closely. Generally, confidence intervals are calculated by using the normal approximation, sometimes preceded by a log transform. We evaluate and compare with analytical approaches: the normal approximation, the log transform, and two binomial methods-the quadratic approximation and a modification of the Clopper-Pearson exact method. We evaluate these confidence interval methods for use with the maximum likelihood and jackknife estimators of the relative frequency. Our results show that confidence interval construction with maximum likelihood point estimates is more accurate than construction with jackknife estimates. When using maximum likelihood estimates, the normal approximation produces acceptable two-sided confidence intervals, with the smallest length, at alpha = .05. At alpha = .0 1, the normal approximation is anticonservative. In all cases, the normal approximation is unable to produce adequate one-sided confidence intervals. The log transform and both binomial confidence interval methods are shown to be generally superior to the normal approximation. In particular, the modified Clopper-Pearson method produces very acceptable one-sided and two-sided confidence intervals for small replicate culture size.