Measuring the impact of 'tone of voice' in interactive marketing

Over the years, I've spent a lot of time arguing with clients about the tone of voice in their communications, and in the end, I decided not to pursue work as a copywriter. I'm not a playful writer but I'm committed to being accessible, using down-to-earth and conversational language. Clients seem to think I was devaluing their products and services by not being serious enough. And I just hated writing boring, pompous stuff. 

Now the Nielsen Norman Group has produced some research over the tone of voice used on web sites, finding that casual, conversational tones performed best most of the time. (Of course, casual is wrong in some cases but conversational is almost always good.) 

Nielsen Norman Group: The Impact of Tone of Voice on Users' Brand Perception, 2016-Aug-7 by Kate Meyer

In a two-part study, we tested pairs of nearly identical website content. In each pair, the only aspect that we varied was the tone of voice used. We found that there are indeed measurable effects of tone of voice on users, specifically on users’ impressions of an organization’s friendliness, trustworthiness, and desirability. We also found that a user’s impression of an organization’s trustworthiness is a strong predictor of their willingness to recommend that brand. ... 

Across all of the tone samples tested, we saw that casual, conversational, and moderately enthusiastic tones performed best, though they do not necessarily need to be combined. ...[A] conversational but serious tone can be successful for a bank.

Choosing a tone of voice is a tricky game of balancing your brand’s personality and priorities. There’s no one solution for every situation.... [I]t’s possible to choose a tone that makes your brand seem friendly, but still doesn’t make your potential customers more likely to choose you.