private double inverseCumulativeProbability(int n, double p) {
        if (p == defaultP && (n >= MIN_N) && (n < defaultCumulativeProbability.length + MIN_N)) {
            return defaultCumulativeProbability[n - MIN_N];
        }
        return computeCumulativeProbability(n, p);
    }
Use StudentT distribution and estimate how many hits you need from each partition
to to get the globally top-k documents with the desired probability

@author baldersheim
container-search/src/main/java/com/yahoo/search/dispatch/TopKEstimator.java