5-4.10 Compound surname by marriage.

Another specific case to consider is a person who carries a name such as "Barker-Cuthbert" for a surname. What are the consequences of viewing this as two surnames? Maybe some record keeper analyzes this surname into two pieces and chooses one of them to record. In this case there seems little difficulty in estimating a value specific comparison weight of "Barker-Cuthbert." There would be a moderate weight for <Barker> and another one for <Cuthbert>. The sum of these two weights would be comparable to a single high field weight, quite like we would guess that <Barker-Cuthbert> ought to be. But two common names would weight too little together, and two very rare names would be more like having two field weights.

The key to combining the weights is the realization that it is the coincidence value, not the reliability that needs adjusting. The coincidence (c) for a combination of names ought to be the product of the coincidences of each component name (c1 × c2).

aw = log2 [r ÷ (c1 × c2)](5.8)
dw = log2 [(1 – r) ÷ (1 – [c1 × c2])](5.9)