1. A computer-implemented method for estimating a click-through-rate for at least one content item to be placed on a rendered page, the content item having a plurality of available content item types and the page having plurality of available content item placement positions, the computer-implemented method comprising: determining a reference context associated with a combination including a particular content item placement position and a particular content item type; collecting performance data for the reference context; determining a click-through-rate for the reference context based on the performance data collected; determining a click-through-rate for at least one additional context on the page relative to the click-through-rate for the reference context, the at least one additional context being associated with a different combination than the reference context; collecting performance data for the at least one additional context; determining an actual number of impressions of a particular content item in the additional context based on the performance data collected; normalizing the actual number of impressions of the particular content item to any context on the rendered page; and determining a click-through-rate estimate for the particular content item in any context on the rendered page.