By Hal Hodson (Image: Noah Manneschmidt/CC BY-SA 2.0) Millions log into Reddit every day, letting fly with cat pics, tales of social awkwardness and Star Trek references. This is the war for Reddit “karma points”: the crucial upvotes and downvotes from internet strangers, which govern how content is displayed across Reddit. A user’s karma score, displayed next to their username, reflects how much other people like the things they have submitted. Make no mistake, it’s a serious business. Now computer scientists from Stanford University in California have put Reddit under the microscope. Their goal is to understand what user-controlled factors, beyond the content itself, contribute to a post’s success – and the acquisition of karma. “There’s a very high chance that your content will get missed out on Reddit,” explains lead author Himabindu Lakkaraju, who will present the work at the International AAAI Conference on Weblogs and Social Media in Cambridge, Massachusetts, on 17 July. “We basically asked whether branding is important on Reddit, and it turns out it is.” To explain how titles, community and timing affect posts’ popularity, Lakkaraju analysed an archetypal Reddit image – a painting of a roaring bear, sporting a top hat and monocle and grasping a tattered American flag, riding on Abraham Lincoln’s back. Lasers shoot from Lincoln’s eyes. It is perfect Reddit content. The image’s first submission, to the “pics” subreddit under the title “I’m not sure I quite understand this piece”, garnered just 62 karma points. Subreddits are where people post submissions that pertain to a specific character. But one year later an opportunistic Redditor was 10 times as successful in the “funny” subreddit, with the simple title, “MURICA”. To figure out what’s driving these kinds of differences, Lakkaraju and colleagues analysed a set of 132,000 submissions. For starters, they found that each image on Reddit was resubmitted an average of seven times. They also found that Reddit has a memory, and it’s about 45 days. The chances of negative reactions to reposted content becomes much milder after that point. There are optimal times to post too. Lunchtime is best for the most popular subreddits like pics, gaming and atheism. The team also found that some subreddits work much better for cross posting than others: reposting from “gifs” to “space” is a good idea, while “funny” and “gifs” tends not to work so well. The team took the analysis further by training a machine learning algorithm on the most successful posts in their dataset, measuring which words and combinations of words were most often associated with successful posts. This led the team to predict the popularity of Reddit posts fairly accurately, although they tend to underpredict the largest popularity spikes. Lakkaraju says that content is important, but can only take a post so far. “People want to get things noticed in the community very badly,” he says. “So they think: ‘What can I do to account for the other factors so that my content gets noticed as much as possible?