If I have an adgroup that has a low CTR would deleting and recreating it reset the CTR or does Google remember the keywords and their CTR? Of course I would name the campaign and adgroup different then the first time as well as use different copy. Thanks!
The way I understand it is that your whole account has the CTR recorded. Kinda like the way you can't delete anything from your account. Also I believe quality score is only related to the landing page in question. (Notice how Google makes sure tot ell you that using the content network won't affect things)
But if the clickthrough rate is reset, won't this 'repair' the quality score? It's not exactly a long-term solution, since your clickthrough rate will be exactly the same as it was before, so you'll end up back where you started very quickly... Why not just improve your quality score by writing better adverts?
The quality score also uses landing page quality and ad relevance, both of which are unaffected by an improved CTR.
Quality score of the account / campaign / ad group is also affected by history, which is very much affected by a high CTR. That's why if you have a good ad group after a while your bids will start dropping without making any changes to your landing page.
The new adgroup will start fresh with fresh CTR and QS. Now it's upto you... if you still want to repeat your mistakes in past performance, the CTR will again be less. Try to optimize your ad copy. All the Best!