Traditionally, blog themes have placed the form to leave a new comment below the listing of existing comments. This still holds true in most WordPress themes to date. However, many sites now have the comment form above the comments. Notable sites include Mashable and Reddit.
I was pondering the reasoning behind this recently. The obvious answer is that it encourages more comments, as someone who just finished the article is prompted to post while the content is still fresh in their mind. Meanwhile, having the form below the comments requires that a user read (or simply scroll past) others’ messages—perhaps even seeing like-minded comments and deciding against leaving one.
Assuming this is true, you could promote a higher volume of comments by placing the form higher up, or on a higher traffic site, promote a higher quality of discussion by putting it toward the end. I assume someone has done tests, but I couldn’t find any publicly-posted results.
Thoughts?
Automattic, the company backing the WordPress blog platform, recently purchased the hosted commenting system 
Disabling Comments on Old Posts, or How to Kill Discussion
May 1, 2012 by Matt | Posted in Blogging No CommentsGuess which posts on this site receive the most new comments every week. Older ones. Not the latest posts, but the ones that have stood the test of time and still have people looking.
The terms sometimes used to refer to posts that remain relevant, and bring in traffic, for years are “evergreen content” and “pillar content.” I have posts that are a few years old, are still the most popular in terms of traffic, and gain a couple new comments every month. Occasionally a spam comment will appear on those posts, but they’re outnumbered by legitimate comments, continuing a discussion that has been going on for a long time. Does it really make sense to put an end that, and frustrate readers who arrived a little late but still have questions to ask or opinions to voice, just to avoid a few spam comments Akismet happened to miss?
That seems like a wasted opportunity. Instead, you could update your evergreen posts to remain relevant, and add some links to more recent posts on the same subject. Build user engagement and keep the discussion going.
Smaller blogs, especially, can’t count on timely social media-driven traffic. They tend to succeed more with long-tail traffic from search engines. Obviously you won’t get very many comments at all if the form gets disabled just when a post is becoming popular…
Fortunately, there is a nice middle ground. Some posts, especially ones that have attractive keywords in them but become less relevant later down the line, rarely see legitimate comments but are magnets for spam. I have a couple that seem to get a handful of spam messages that sneak past Akismet every week, but never have real comments anymore. With those kinds of posts, you could probably toggle the discussion off without inconveniencing anybody but spammers.