Halliday (2008: 161):
Grammatical intricacy can be measured as the number of ranking clauses in the clause complex. But this is more problematic: partly because it requires criteria for identifying the limits of a clause complex in spoken discourse, and partly because it makes no sense to calculate it as a mean. The reasons for this have nothing to do with the way spoken language construes experience; they are not ideational but interpersonal. Spoken language is inherently dialogic in nature, with very many short turns guiding the interaction; whereas intricate clause complex structures can only occur in the more monologic interludes in the dialogue. Thus the mean figure for intricacy would be essentially meaningless.