Looking for a top-rated movie or a captivating new book? Chances are you’ll check a few reviews first. You probably give some more weight than others, but why?

What makes a good review?

New research from Waipapa Taumata Rau, University of Auckland suggests more formal reviews are generally considered more helpful.

Formal language is marked by precision, clarity, minimal self-reference and persuasiveness, and the study suggests it makes people take note compared to informally written reviews, typically resembling spoken conversation.

But there's a catch, according to the paper published in the European Journal of Marketing - become too formal and perceived helpfulness starts to decline.

Business School researchers Dr Shohil Kishore and Associate Professor Laszlo Sajtos analysed over a hundred thousand movie and book reviews across retail site Amazon and non-retail sites Google and LibraryThing, which is a community-driven book review site. Their analysis considered ‘helpful votes’ from readers.

“The key takeaway is that there’s a sweet spot,” says Kishore, “being too informal online can make a review less useful to others, but being overly formal can have a similar effect.”

He says understanding what makes a review helpful is important for both online platforms and sellers, with previous research showing Amazon books with more ‘helpful votes’ on their reviews tended to have higher sales.

“To the best of our knowledge, this is the first study to contrast the linguistic styles of online reviews for movies and books across retail and non-retail platforms,” says Sajtos.  

For movies, the academics looked at 67,560 Amazon reviews and 31,517 Google reviews of the same 94 films, including blockbusters like Jaws, Finding Nemo and The Matrix.

For books, they compared 4,409 Amazon reviews with 3,462 reviews on LibraryThing of the same 53 titles, including bestsellers, children’s literature, science fiction, mysteries and classics.

They say Google movie reviews were typically shorter, less formal and used simpler language than those on Amazon.

Amazon movie and book reviews were already around the level of formality associated with greater helpfulness, while the findings suggest Google movie reviews and LibraryThing book reviews could benefit from increased formality.

“Amazon reviews, especially book reviews, already exhibit high formality and are more difficult to read, which limits the marginal benefit of further increases,” they write.

“LibraryThing, shows formality and complexity levels comparable to Amazon, yet readers still respond positively to more formal writing.”

They also say formality had a stronger influence on perceived helpfulness than two other features of writing previously studied in online reviews: complexity and readability.

The three measure different things. Formal text is “precise, lucid, eloquent and persuasive”.

Complexity includes factors such as the diversity of words and sentence structure, while readability is concerned with how difficult it is for a person to process the text, including word and sentence length.

The study suggests formal reviews that emphasise objective content and descriptive clarity, while minimising personal, context-specific details, such as who someone watched a movie with or where they read a book, are beneficial for readers.

So, if you want your review to have impact, focus on clear, objective information that will be useful to other readers, says Sajtos.

“Avoid too many personal details or first-person statements and concentrate on the book, movie, product or service itself.

“Online platforms might also help by encouraging this approach when people write reviews, with prompts or real-time feedback that steer reviewers towards clear, broadly relevant information.”