I've been wanting to get back to this discussion, as I'm seeing that it may be making some members believe that simply making an article 3,000 words long may suffice for it to rank or even be treated as an "in-depth article"... and I feel compelled to say that, IMO, that's an overly simplified view. I also doubt it's likely that we're going to see many articles on ecommerce sites promoted to in-depth status, but there are some examples of long and thorough ecommerce articles, not officially called "in depth", that rank very well, and I'll discuss them at the end of this post. "In-depth articles" in Google serps...
The articles that I've seen which Google classifies as "In-depth articles" in the regular serps usually originate in extremely well-known publications... The New York Times, Wall Street Journal, The Economist, Washington Post, BBC, etc. They are for broad searches... one or two words... and even on the several I've seen about products, they seem to occupy a different mind-space from typical ecommerce articles. Often they're subjects of world import.
All that I've seen that are specifically called "In-depth articles" are at the bottom of the search page, generally in positions 8, 9, and 10, lower than where you'd like an ecommerce article to rank.
They're also written by widely acknowledged experts in the field. It's worth noting that back in March, Barry Schwartz reported in Search Engine Roundtable that Matt Cutts had tweeted to confirm that "Google uses a form of author rank or author specific authority in the in-depth articles ranking formula"
.... Google's Cutts Confirmed That Author Authority Is Used For In-Depth Articles Barry Schwartz - Mar 13, 2014
I don't think the above has previously gotten mentioned here.
Regarding length... I doubt there's any one-size fits all formula. Keep in mind the expectations of the reader you expect to engage with the material. I've always felt that certain topics simply demanded longer articles, and anything much less was simply fluff. There's also a certain kind of "gravitas" that a longer article conveys... but your writing and content need to sustain that... and the subject needs to have an audience willing to spend the time absorbing it.
It's also often the case that extremely long articles can be helped by being split up into segments... providing more exposure to sections, particularly if titles are adjusted to describe the subtopics. The article breaks can provide manageable equivalents of "chapters" for online reading.
In our discussion about in-depth articles in this thread, topics like length, audience, markup, etc, were touched upon.... In-Depth Articles - Only for Brands and Google ? Or for Everyone? Aug 2013 http://www.webmasterworld.com/google/4599873.htm
I'd say the most common format I found was the 8,000 word article that was broken into roughly five 1,600 word pages. In general, segments of between 1,000 to 1,600 words were typical. That said, I've come across at least one news
article of c350 words that was classified in the news results as in-depth, a classification I felt was not very accurate... but perhaps at the time it was the deepest thing around. In-depth ecommerce...
I have a favorite site that features what I consider extremely thorough product reviews which generally run between 10 to 20 pages, broken into well-defined and extremely clear segments. It's an affiliate site... and, typically, its reviews get top rankings. I've never counted the words... that's not the point. The content is comprehensive and completely absorbing, so much so that many people in the field follow the reviews even if they're not planning to buy the particular product. They follow the site just to follow the state of the art in the field.
I think that the architecture and thoroughness of the articles is certainly more important than the word count, and the quality of the information directly contributes to the reputation of the site. The reviews are also well illustrated, and the articles are also extremely well-edited.
This particular site is not an easy type of site to generate on a low budget, but I think its approach can be emulated in some areas by those who put in the effort.
Worth noting that many sites that got hit by Panda had knowledgeable material, but the writing was simply not good. The material wasn't well-organized or well-edited, and was often repetitious... and the articles in effect were too long.
I'm curious to see whether some of these will come back with the latest update, or whether further editing will be necessary.