The modal value is simply the most often occurring value or set of values in a given distribution of values or set of values. Compare it to the median value which has half of the distribution above it and half below it. The average or mean value is the sum of the values divided by the number of values. The average can be seriously skewed by a few very large or very small values. So, the modal haplotype is just the most frequently occurring haplotype in a set of haplotypes. (This definition is from John T. Nichols, May 2003,
[email protected]; permission granted.)