Have you seen the little “i” in a triangle icon on some of the ads? When you hold your mouse pointer over it, it brings up some text saying “Ad Choices.”
Contextual ads show ads based on the content of the page being viewed. Interest based or behavioural ads show ads based on your online activity and browsing history.
There are a number of problems with interest based ads. The first is that they assume that only one person is using the computer. This is not always true, especially in households where multiple people use the same computer, so you can end up seeing ads that have absolutely nothing to do with your interests. Your children may have been using it to look at toys or do school work; this doesn’t mean that you are going to be interested in ads for Barbie or historical services.
Another is that, even if the ad shown is based on your history, you still may not actually be interested in viewing on the topic. Just because you have visited a certain type of site does not mean that you are actually interested in ads for that type. For instance, even though you use your computer for online banking this doesn’t necessarily mean that you are interested in changing your bank. You are also highly unlikely in this case to click on an ad for your bank. You may have been looking at a certain product doesn’t mean that you will click on an ad for it. For one thing, you may have already purchased the item. You may also just be carrying out research.
Rather than showing an ad based on something that they think you want, it can be better to show ads to do with the topic of the article – which is something you are looking at at the time with presumably at least some interest.
You can personally opt out of many interest based ads, as you may not want advertisers targeting you like this. Clicking on the “i” icon or the “Ad Choices” text should take you to a site where you can opt out (such as http://www.youronlinechoices.com). It may be a site specific to your country, or an advertiser’s site, such as AdSense Help.
Publishers can also opt out of displaying interest based ads on their sites, and many do as they believe it’s better to show an ad based on what the user is actually viewing, rather than on something they may have viewed in the past.