Google has long made the statement that when examining CTRs for calculating quality score, only the CTR on Google.com was used (which was normalized by position).
Now that quality score is being factored in real time, it makes sense to change that rule slightly.
The CTR used in determining the quality score for search will be your CTR on that specific site. Therefore, if your ad will be shown on Google.com, as with the past, your CTR on Google.com will be used.
If your ad is being displayed on Aol.com; then your CTR on Aol.com will be used in calculating your quality score.
Overall, a pretty minor change – but one that’s worth nothing how some of the ‘makes sense’ factors on quality score will now be possible with the real time calculation.