digraphs and sorting

[Gary Holton]

Hello,

I know this list doesn't get a lot of traffic, so apologies in advance
for spamming you with this query. For years I've accepted without
question the orthodoxy which sorts dictionary entries by digraph
rather than by single characters. This makes obvious sense, since
digraphs such as th or even trigraphs such as tł' are single phonemes
and hence shouldn't be relegated to secondary status within a
dictionary. On the other hand, we also know that many languages do
just fine treating digraphs as separate characters for the purposes of
dictionary sorting (e.g., English has no "th" section; Malay has no
"ng" section). So, my question is, does anyone know of any usability
studies -- or even just subjective account --  comparing the relative
advantages of each approach within a language maintenance situation?

Gary Holton