Are there any empirical studies showing that the quality of the writing in a brief has an effect on its success?

In general, the answer is no, but I’d like to highlight another important article on a related subject.

The author asked judges to choose which of two versions of a legal argument they considered more persuasive. Half the judges chose between a traditionally worded (legalese) argument and a simpler, plainer (plain English) version. The other half chose between the legalese version and a version that used first person, contractions, and so on (informal). The study collected responses from trial and appellate judges in state and federal court and sorted results by those criteria and by age, experience, sex, and geographical setting (rural or urban).

Some results:

On average, judges considered the plain-English version more persuasive than the legalese version 66% to 34%. Federal appellate judges chose the plain English version 77% to 23%.

On average, judges considered the informal version more persuasive than the legalese version 58% to 42%. Female judges chose the informal version 83% to 17%, and rural judges actually chose the legalese version over the informal version 55% to 45%.

The full article is worth reading, and I’m pleased to say that I helped the author with the project when he was a law student.

Sean Flammer,  Persuading Judges: An Empirical Analysis of Writing Style, Persuasion, and the Use of Plain English, 16 Legal Writing 184 (2010).