you may be a reliable democratic voter in a solid-blue city. maybe you have a graduate degree; maybe you<u+2019>re a member of an ethnic or religious minority; maybe you are a woman. any of these would make you a likely hillary clinton supporter. so why did you just see an ad for donald j. trump <u+2019>s presidential campaign on facebook ? the new york times has collected an extensive database of political facebook ads, and data about how they are targeted, from our readers as part of our political ad tracker project . microtargeted online advertisements can be a powerful tool for political campaigns to tailor a message to specific people they are trying to reach. but the reason you saw a particular campaign ad on facebook may have nothing to do with your political views, or even your demographic profile. it could depend on whether you live in a swing state and on your internet activity <u+2014> or be practically random. you can find the reasons you were shown a particular ad, political or otherwise, on facebook with just a few steps. here<u+2019>s how: <u+2022> first, find an ad in your facebook news feed. <u+2022> then, in the upper right corner of that ad, find the small v-shaped gray arrow and click it. <u+2022> a menu will appear with a button that says, <u+201c>why am i seeing this?<u+201d> click it. <u+2022> a pop-up will appear with an explanation of why the advertiser chose to show you that ad. advertisers get the most for their money by sending their ads to people most likely to be receptive to them. but some ads are very broadly targeted. lisa klepper tannenbaum, a suburban new jersey woman who is a registered democrat and likes mrs. clinton<u+2019>s facebook page <u+2014> she even volunteers for her campaign <u+2014> saw an ad seeking donations from mr. trump on her facebook feed between family photos and updates from long-lost high school classmates. <u+201c>what actions have i taken, what sites have i visited, that would make someone believe there<u+2019>s even a remote possibility i would support donald trump?<u+201d> ms. tannenbaum said she wondered. one possible explanation is that mr. trump<u+2019>s campaign has run some ads to be shown to anyone older than 27 in the united states. brad parscale, the digital director for the trump campaign, said the campaign had tested many combinations of demographic criteria to raise the most money while spending less on ads. the campaign<u+2019>s online donors tend to be older than 27, he said, adding that younger people, who are less likely to donate, may be shown fewer fund-raising ads. here are some other reasons you might see a candidate<u+2019>s ads: the campaigns have your email address . the campaigns have uploaded to facebook lists of email addresses that supporters have provided online, while donating money, or at rallies. these lists may be sliced and diced by the campaigns according to geography, race, gender or more esoteric data purchased from commercial brokers. facebook then matches each email to the correct facebook page, assuming the supporter is one of the roughly 200 million americans with an account. advertisers, including the trump campaign, have used this targeting mechanism to encourage a subset of their supporters in swing states like north carolina and florida to request an absentee ballot. facebook thinks you resemble the candidate<u+2019>s supporters. both campaigns have made extensive use of an opaque feature called <u+201c>look-alike audiences.<u+201d> this feature finds users who have facebook fingerprints <u+2014> demographic profiles, histories of <u+201c>likes<u+201d> and clicks <u+2014> that are similar to people who already like the candidate<u+2019>s facebook page. these potential supporters then see the ad. the candidate does not directly get a list of names, but the clinton campaign has run ads to <u+201c>look-alikes<u+201d> asking them for their email addresses so that it can directly reach them via email later. your political leanings. some ads have been targeted based on how facebook has classified your political beliefs <u+2014> on a scale from <u+201c>very conservative<u+201d> to <u+201c>moderate<u+201d> to <u+201c>very liberal.<u+201d> it makes these judgments based on some obvious clues, such as which candidates<u+2019> pages you <u+201c>like,<u+201d> and some not so obvious. if you <u+201c>like<u+201d> the same shoes or cars that many liberals like, facebook might peg you as a liberal, too. your age or ethnicity. even if the campaigns do not know your email address and facebook cannot figure out your political leanings, you might see ads if the details of your demography signal what camp you are in. those recently targeted by the clinton campaign have included ohioans between 18 and 34 years old, and african-americans in florida and pennsylvania, groups in which she might find valuable new voters. (facebook does not ask its users their race, but it does let advertisers show ads to people grouped by <u+201c>ethnic affinity<u+201d> who <u+201c>like<u+201d> content that might interest a particular ethnic group.) your browsing history. visiting a candidate<u+2019>s website can prompt an ad to be shown to you the next time you log on to facebook. many campaign sites include small pieces of software from facebook or other networks that record who visited the site. this technique, called retargeting, is not unique to politics; you may have comparison-shopped for a computer or other big-ticket item and then discovered that ads for that exact item seemed to follow you around the web for weeks. and it can come across as a personal insult: just as a devoted iphone user does not want to be bombarded with samsung ads, a trump supporter might not want to be hounded by plugs for mrs. clinton. find out what you need to know about the 2016 presidential race today, and get politics news updates via facebook , twitter and the morning briefing newsletter .
why facebook showed you that ad for the candidate you hate
jeremy b. merrill