One way to save data for Affiliates is to save direct traffic.  This literally saves all web traffic directly to the database.  The saved traffic  is the visitors who get to your shop by using your URL in their internet browser.  This would normally put a large strain on database the server and therefore, not typically recommended.  The following article explains how to enable the option to save direct traffic in PrestaShop 1.5.

How to Enable Save Direct Traffic in PrestaShop 1.5

1. Login to the Administrator as an Administrator
2. Hover over menu bar where it says STATS - click on REFERRERS when it appears at the bottom of the drop-down menu.
3. You will see the following screen:
   
   
   
   
   Click on the radial button for YES or click on the radial button for NO in order to activate or disable this option.  As per the note do not enable unless you are sure that your database server will be able to handle the increased load.
4. Click on the SAVE button in the bottm left corner to save your entries.

Saving the direct traffic basically saves all visitors  coming into your site causing a huge increase in database server traffic.  If you are not sure if your database server can handle the increase in traffic, then consult with your technical support team to see if there is a need to upgrade your servers.