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It would make sense that the algo becomes different for industry sector, to better tweak interpretation of true content, relevance, spam.
One algo fits all can't be very precise.
It then follows, one seo strategy fits all can't be very effective.
I noticed ranking for sites in one major industry sector dropped, but ranking for sites in other major industry sectors did not.
I assume you mean CHANGED, not dropped. Because rankings for an entire industry cannot drop. Your sites can drop or raise, but it seems like you are saying you have noticed more of an impact in certain industries.
This very well could be, but I doubt it is industry specific. It could be related to how competitive of a search term you are searching for. If there are 4 million results, then more factors may be factored.
Also, G may be manually altering some SERPs. It is possible they look at the most highly searched for (or even more likely - monetized SERPs) and apply certain tweaks to them).
Maybe they are looking at the highly monetized SERPs and applying something similar to TrustRank [webmasterworld.com]
I can imagine that for some industries (like travel) extensive external links are a tweaked negative, whereas this does not weigh on other industries (say wellness).
Keyword density may be tweaked to higher requirement for say the medical industry, normal requirement for other industries.
Incoming links tweaked higher for education industry, normal for other industries.
Just wild examples.
Authoritative sites and PRank seems to be have been the criteria, but PRank seems to have lost relevance (many sites with lower Prank now appear above sites with higher PRank). The method of determining "authority" and "relevance" may now be being tweaked according to the topic, or industry.
Lots of content rules the waves, beyond content, which criteria should the algo let prevail?
The word is Allegra's purpose was to reduce spammers, meanwhile we see Prank decrease in its apparent importance (its spammable after all).
Reports here in WW are some sites affected, others not, others improved by the algo change.
Sites by a same or similar acting webmaster using a same or similar strategy (28 steps, whitehat, grey, blackhat, whatever).
Just a thought that the algo has changed according to the topic or industry.
That would explain some up, some down, for one-size-fits-all "optimized" sites ("optimized" for their industry keywords).