The key message from a new study isn't "those Strategies won't make you happy" as much as "we have weaker evidence for it at the moment than you might realize." Taking a 5-mile run might just sound like hell for many readers, but it goes a long way to improving my mood. If I'm stuck on a particularly difficult story, in never-ending Zoom meeting hell or frustrated from staring at a screen for the day, chucking on some Nikes and trotting around the neighborhood seems to get me out of the rut. And then when I get home, there's nothing that makes me happier than slamming down a can of Pepsi Max. (Overblown health concerns, be damned!) A double dose of joy in the day. My anecdotal evidence for the mood-boosting abilities of exercise is backed up by thousands of websites with a raft of strategies that will make you happier. For instance, our sister site Healthline presents 27 habits that can help you "be happy." These include things like smiling, breathing deeply and acknowledging unhappiness. Exercise is on the list, too.But a new systematic review, published in the journal Nature Human Behaviour on Thursday, suggests the scientific evidence for some of the most commonly recommended happiness-boosting strategies is fairly weak. That's not to say the strategies don't work, just that scientists know less about who they might work for and when they might work than people think.The researchers behind the review — Dunigan Folk, a psychology Ph.D. student, and his professor, Elizabeth Dunn, at the University of British Columbia — first conducted an internet search to determine the five most common strategies being recommended in the media when people searched via Google with terms like "how to be happy" and "happiness strategies." That produced a list of websites offering up advice, including Healthline, WikiHow, Forbes and The New York Times and helped identify the top five: showing gratitude, socializing, mindfulness and meditation, physical activity and exercise, and spending time around nature. Taking to the scientific literature, Folk and Dunn were able to identify more than 500 studies that had examined the strategies in nonclinical settings. However, only 57 of these studies were either "preregistered" or contained a large enough sample size to assess the strategies comprehensively. Preregistration is a strategy psychologists and other scientific disciplines use to publicly document their study plan. It's suggested this helps reduce false positives and, in the new review, is taken as an important component of how strong the evidence in a particular study might be. Using their collection of 57 studies, the pair examined the science underpinning the top five strategies, finding there was some evidence that expressing gratitude and social interaction can improve happiness, but far less evidence for exercise, mindfulness and meditation, and exposure to nature. Does that mean these strategies don't make us happier and don't work? No, that's not what Folk and Dunn are getting at. "We certainly do not mean to imply these strategies are akin to snake oil," said Folk. "There are plenty of good reasons to think they improve mood, and they almost certainly improve mood for some people."He stresses this particular review wasn't examining the evidence for particular strategies and how they might help certain groups of people. For instance, if a study was looking at how exercise helps people with chronic weight problems feel happier, it wasn't included here. "It's very possible there is high-quality evidence that some of these strategies are effective for different clinical ailments like anxiety disorder," he said.The key message isn't "this won't make you happy" as much as it's "we have weaker evidence about how to make ourselves happy than you might have seen online." Folk and Dunn also point to the urgent need to conduct better experiments that are both preregistered and have sufficient sample sizes to understand how good these strategies are.While expressing gratitude does appear to be useful for improving happiness in the two adequately powered and preregistered studies cited in the review, the benefits are short-lived. The two studies had American parents or undergraduates write a gratitude letter, comparing those with writing about what they did last week or a list of daily activities. The review authors concluded that "gratitude practices can increase mood, at least temporarily." That's something CNET wrote about in a "Try This" tips article awhile back, following a 2005 study which suggested writing down three things you're grateful for each day. In the review by Folk and Dunn, the researchers found this particular study was not adequately powered or preregistered. It doesn't mean that the strategy won't help people, just that we should be conscious of the fact that "how to be happy" articles might not have all the answers — because not even the experts do!And for what it's worth, Folk says he's an avid exerciser and believes it boosts his mood. Writing the paper hasn't changed that. He also likes hanging out with friends, playing the piano and reading fiction. These things, his experience tells him, boost his mood. That might not be it for everyone. "I think people should see what science recommends, give the strategies a try, and go with what works for them," he said.I'll stick with running and Pepsi Max, thanks.