Researchers claim that ending a text message with a period makes it come across as insincere. But the study behind the claim raises some questions itself.

A team led by Celia Klin of Binghamton University asked 126 undergraduates to look through message exchanges displayed on phone screens and as handwritten notes on paper. They were then asked to say how sincere the reply seemed.

Each of the 16 messages consisted of an invitation and then a one-word positive reply such as “Okay” either with or without a period at the end.

According to the findings, published in Computers In Human Behavior, when the test subjects were looking at text messages, they were more likely to rate a message as sincere if it did not end with a period. This distinction wasn’t apparent in the handwritten exchanges.

Klin made the well-established point that reading a text message leaves users searching for contextual cues that they can’t get from body language or voice tone, and that this means users placing more emphasis on the minutiae of the message. However, she didn’t offer a clear explanation of why a period should have a negative result.

In in a follow-up test, the findings of which aren’t yet published, it turned out that ending a reply with an exclamation mark made it appear more sincere than having no closing punctuation.

The study does have some obvious limitations. Using undergraduates means the test panel will largely have been drawn from a limited age range and likely a narrow social background compared with the population as a whole.

While having a one-word reply in the message was clearly a way to try to isolate the effect of the period, it means the study doesn’t really tell us how significant the inclusion or exclusion of the period is in general. For example, a reader might perceive a difference in sincerity (either way round) between “Yes, I can come” and “That sounds amazing, I’d love to come” that overrides any effect from the use or non-use of a period.

Having a positive reply could also distort the results. It would be much more interesting to see whether the absence or presence of a period affected the perceived sincerity with more ambiguous replies to an invitation such as “I’ll try to come” or “I’ll come if I can.”

The study format also means we don’t know if the “period effect” would still be detectable with longer sentences. It’s certainly possible that, while “Yes.” is a perfectly valid sentence, people may perceive the inclusion of a period as unusual or overly formal in a way that they wouldn’t do with a longer sentence that followed the more familiar subject, object, verb model.

And of course running this study in isolation means users aren’t familiar with the relationship between the texters. In real life, we get to know the pattern of the way people use language in their texts and can often perceive insincerity from a change in that pattern, whether that be a message being unusually terse or implausibly eloquent and detailed.