Performance of the lot quality assurance sampling method with 80% or more infants in their catchments area receiv- ing DPT1 can be considered as performing adequately. While the EPI centres with a coverage rate of 50% or less ought to be considered as inadequately per- forming and be identified for attention, the ones in the mid-range of 50-80% may be considered somewhat adequate, and for the time being no special attention is needed. Using these information, probabilities of detect- 39 ing ‘adequately-performing’ or ‘inadequately-perform- ing’ EPI centres can be calculated. Table 1 presents such probabilities along with provider and consumer risks for various combinations of sample sizes and maximum al- lowable unimmunized infants in the sample. The probabilities in Table 1 were calculated using the binomial formula. In each case, the upper and the lower threshold of the triage system were 80% and Table 1. Example of application of the LQAS method to detect the probability of 80% or 50% coverage of health- area residents with respect to vaccination according to various sample sizes and number of unimmunized children Sample size (n) No. in the sample un- immunized (d) Probability of detecting health areas with 80% coverage as adequate (a) Probability of detecting health areas with 50% coverage as inadequate (b) Provider risk (1–a) Consumer risk (1–b) Total clas- sification error (1–a)+(1–b) 8 0 0.17 1 0.83 1 0.50 0.96 0.50 2 0.79 0.83 0.21 3 0.94 0.64 0.06 12 0 0.07 1.00 0.93 1 0.28 1.00 0.72 2 0.56 0.98 0.44 3 0.80 0.93 0.20 4 0.93 0.81 0.07 5 0.98 0.61 0.02 14 0 0.04 1 0.96 1 0.20 1 0.80 2 0.45 0.99 0.55 3 0.70 0.97 0.30 4 0.87 0.91 0.13 5 0.96 0.79 0.04 19 0 0.01 1 0.99 1 0.08 1 0.92 2 0.24 1 0.76 3 0.46 1 0.54 4 0.67 0.99 0.33 5 0.84 0.97 0.16 6 0.93 0.92 0.07 7 0.98 0.82 0.02 28 5 0.50 1 0.50 6 0.68 1 0.32 7 0.81 0.99 0.19 8 0.91 0.98 0.09 9 0.96 0.96 0.04 10 0.99 0.90 0.01 *Optimal decision rule for a sample size; LQAS=Lot quality assurance sampling Source: Grant EL, Leavenworth RS. 1988:391-425 (7) 0 0.04 0.17 0.36 0.00 0.00 0.02 0.07 0.19 0.39 0 0 0.01 0.03 0.09 0.21 0 0 0 0 0.01 0.03 0.08 0.18 0 0 0.01 0.02 0.04 0.10 0.83 0.54 0.38* 0.42 0.93 0.73 0.48 0.28 0.27* 0.41 0.96 0.80 0.56 0.33 0.22* 0.25 0.99 0.92 0.76 0.55 0.34 0.20 0.15* 0.20 0.50 0.32 0.20 0.11 0.08* 0.11