I'm gonna _blank - use it to convert better
We're all familar with the little bit of HTML code, TARGET="_blank" and how annoying it can be if misused. For newbies, it's the command that tells the browser to open a link in a new window rather than opening the link in the same window (default browser behavior).
There are times when you can improve your conversion rates by implementing the new window command sparingly and for the right type of links. Use it too much, however, and your visitor loyalty will suffer.
First it's important to understand typical visitor behaviour. Let's have a quick look at what happens when a visitor navigates away from your site by clicking on another site link. With the default link style the visitor is going to either click the back button, or start reading content on the new site and forget all about the last one. What happens next depends entirely on whether the new page or previous page is more interesting for the reader.
With the the new window link behavior the visitor is either going to close the new window or maximize it and start reading the content. Either way, the original site (your site) will still be displayed in the original browser window. The reality is, people are a lot more likely to close a new window rather than click the back button simply because a new window just feels like spam.
Ok, that's nice to know but how does that help us convert more traffic? Here are the times you should and shouldn't open links in a new window, and why.
The best thing that can happen when you have pay per click links is for every single visitor to click on every single link. Therefore you want your visitors to stay on your page of links as long as possible. Open each link in a new window leaving the original window open for more clicks. Unfortunately most PPC programs are now served up with scripts, Google Adwords, for example, which won't allow you to control link style.
Revenue Share, PPA, and every program but PPC
Don't ever open a new window with these sponsored links. What you want to happen, instead, is for the visitor to forget all about your site and purchase products and services from your sponser. If you leave your site window open it'll just tempt the visitor to do something other than pull out their credit card.
Deciding how your partner links should open is a little tricky. Essentially there is no reason why you want your visitor to navigate away from your site after the click. It would follow, then, that you would open all these links in new windows. Despite that fact don't forget that new window equals spam to many people. If you have a lot of partner links consider leaving the default link style (open in same window) as is. Not only will it make your site seem more professional, but will make it more difficult for visitors to distinguish between ads and partner links. A rule of thumb I use is that if you place partner links and ads in the same list they all should have the same link style.
This one is clear cut. Always open new pages of your site in the existing window. The only exception is if you need to load a form for the visitor to complete, such as login or registration forms.
A side effect to using "open in new window" links is that the apparent time spent on your site by each visitor will increase which helps your Google stats.
If you're still not sure what will work best on your site try links both ways and then compare your conversion rates and length of time people stay on your page. Just make sure, as with all other market tests, that you don't change any other parameters during the course of the experiment.