During Google’s most recently released English webmaster Q&A session (English Google SEO Office-Hours From October 29, 2021), Google Search Advocate John Mueller addressed a number of questions.
One of those questions had to do with low-quality pages that have the noindex HTML value:
The video below is queued to the 4-minute, 36-second mark, which is where the question of interest was asked:
“Can noindex pages affect Google's evaluation of [a] quality website at a site level--that is, as it's used in core updates? 99% of the pages of this website are relatively lower quality and not indexed, so 300,000 noindex and 3,000 indexed pages.”
I’d like to say that even if your site doesn’t have this number of pages or proportion of indexed to noindex pages, John’s answer may still apply to you.
John’s response (which, for clarity purposes, I’ve edited slightly) included a few pointers for the person to think about:
“So, I think, first of all, the amount of low-quality pages that you're saying yourself are low-quality pages--that feels kind of tricky or problematic to me, just independently of anything with regards to Google core updates.”
The Importance of Quality Pages...Even Beyond SEO
“If you find that you have so many pages on your website that are really low quality (in the sense that they're not good pages, they don't have any useful content on them) then it feels like an opportunity for something to clean up there, because even if we don't index these pages, users might go to those pages and if that's what they build the perception of your site on, and you know that these are bad pages, then that feels like a recipe for people to not want to return to your site.
“So, kind of outside of anything specific to SEO, that feels like something that would be worth cleaning up.”
A Small Misunderstanding
“Sometimes, people see things as being lower-quality just because of technical reasons--for example, if you have category pages and you can filter them and sort them in different ways, you might say, ‘Well, this is lower-quality because it's not actual content.’
“From my point of view, that's more a matter of just technically not interesting content; it doesn't mean that it's actually a bad page, so that might be kind of a misunderstanding there.”
“...We Don’t Take These Pages Into Account”
“But like going back to the question itself, with regards to the core updates and of Google's understanding of [the] quality of a website overall, we don't take these pages into account, so we really focus on the content that we have indexed for a website, and that's kind of the basis that we have with regards to all of our quality updates and all of our quality algorithms and understanding of the website itself.”
“On the one hand, because that's what we're showing in search, so if there's something on your website that we're not showing in search and we're not using it to promise anything to users who are searching, then from our point of view, that's kind of up to you what you do with that.
“The other point I think is a little bit more practical [is] ...that if we don't have these pages indexed and we don't have any data for these pages, then we can't aggregate any of that data for our systems across your website, so from that point of view, if these pages are noindex, we don't take them into account.”
So, despite the fact that it’s a bit of a long-winded answer, I hope that gives you some things to think about, as well as answer the original questions.
A noindex page is a page that isn’t indexed in Google, so Google doesn’t evaluate it.