public static double actualErrorRate(long maxKeys, long bitSize, int functionCount) {
    return Math
      .exp(Math.log(1 - Math.exp(-functionCount * maxKeys * 1.0 / bitSize)) * functionCount);
  }
Computes the actual error rate for the given number of elements, number of bits, and number of
hash functions. Taken directly from the
<a href= "http://en.wikipedia.org/wiki/Bloom_filter#Probability_of_false_positives" > Wikipedia
Bloom filter article</a>.
@return the actual error rate
hbase-server/src/main/java/org/apache/hadoop/hbase/util/BloomFilterUtil.java