Start planning a vacation or business trip today, and you’re probably going to do most of it yourself. Flights, lodging, rental cars, theme park tickets—everything’s easily available online. And an enormous amount of that work, particularly when it comes to choosing a hotel, involves sifting through customer reviews for the information most relevant to you. But it’s hard to know what to trust on the internet and, in this case, what you don’t know can hurt you.

Read between the lines

Understanding hotel reviews might seem as simple as counting the number of stars each patron gifted the establishment you’re considering (usually between one and five). But it’s actually the language reviewers use that matters most, according to a study published in 2016. The researchers analyzed text in 5,830 reviews of 57 hotels in Moscow, Russia, to show that recurring words and the context of the reviews are what’s truly important.

The study’s end goal was to understand the feelings and motivations behind certain words and to find patterns, says Joel Goh, one of the researchers and currently an assistant professor at the National University of Singapore Business School. A prominent motif was the presence of emotion in reviewers’ words, like consistent aggressive language in negative reviews. Another was the recurrence of words such as “free,” “breakfast,” and “clean” linked to positive ratings.

And while this study was meant to be useful for the properties themselves, consumers can also benefit by creating their own spreadsheets to compare review text that touches on specific categories, says Shawn Mankad, assistant professor at Cornell University’s business school and another member of the research team. So if your main needs are cleanliness and location, you should track the number of reviews that consistently use buzzwords associated with those categories as you make your final decision.

It’s also important to pay attention to when positive posts mention individual hotel employees by name, says Erin Green, a travel advisor in Minneapolis. So if you see something along the lines of “Julian was a great help,” that’s a strong indication that the people who work at the hotel are building relationships with guests and are intent on making a good impression, she explains.

Keep your timeline straight as you sort

Depending on the site you’re using, the settings and filters with which you can sort reviews will differ. TripAdvisor has a “time of year” section, for example, where you can select what people had to say at a specific time of year for any given hotel. Or if there are phrases you specifically want to see, you can head to “popular mentions” on TripAdvisor, which includes options such as “close to transportation,” “on-site restaurant,” and “city view.” Both TripAdvisor and Expedia allow you to look at reviews based on who left them (business travelers, solo travelers, or families, for example).

TripAdvisor, Expedia, and Kayak, like many travel sites, initially list reviews chronologically, so it’s important to keep track of how dates have changed as you focus your search via keywords, traveler type, the language it’s written in, or other filters. If you come across a negative review related to something important for your stay (like trouble connecting to the Wi-Fi), but it’s over a year old, look at more current reviews and then search for possible mentions of changes or upgrades to the property. You may also be able to find a thoughtful response from a manager promising that particular issue has been addressed.

Katie Krumpter, a senior financial advisor for New York Legal Assistance Group and an avid traveler, always makes sure to give more weight to reviews posted within the past six months. The Moscow hotel study didn’t cover the timing of reviews, but Goh says it’s a wise additional precaution because negative reviews can alert hotels to issues and prompt them to find a fix in an effort to satisfy even the fussiest traveler. So last year’s one-star resort might be this year’s three-star destination. Just don’t forget to read the words under those stars.