Update June 22, 2020: With no objection and consensus among the mods, we've decided to elevate this to the CM team.
Currently, it takes five votes within 14 days from users with the sufficient privileges to close a question (you can read more of the specifics about closing and reopening questions here in the help center). This is the default across the network.
Recently, Stack Overflow reduced this threshold to three. There is a TON of discussion on that post and others about why the threshold should be lowered, but the ultimate goal was increase the efficacy of individual actions. In other words, when a user with the close/reopen privileges votes, there should be a good chance that this will result in a question being closed/reopened.
Why lower the threshold?
Why does this matter? Imagine that you've voted to close a few questions, hoping to maintain a high quality of questions on the site. You notice that it rarely does any good. Bad questions just sit there until your close votes age out. Why would you continue voting to close? If we lower the threshold, there's a better chance that enough votes will accumulate to close the question, and you'll be encouraged to keep voting.
The opposite is true as well -- if you notice that closed questions are getting edited and improved, but your reopen vote never makes a difference, why would you try? A lower threshold means that not only will more questions be closed -- but more closed questions will be reopened as well!
This will not only help improve the quality of questions on the site, but it also encourages users to edit closed questions, since it increases the chances that those edits will trigger a question to be reopened.
Did it work?
Yes. SO ran a two week experiment where they tracked efficacy (how many questions completed the close/re-open process before the votes timed out) and actioned of count (how many times a close/reopen vote resulted in closing or reopening, respectively). This table summarizes their results:
Basically, when they lowered the threshold, there was a significant increase in the chances that when a user cast a close or reopen vote, the question would eventually be closed or reopened (respectively) before their vote timed out. AND, any vote increased the chances that a question would be reviewed by enough other users to reach a verdict (perhaps a user votes to close but a closure isn't justified -- the lower threshold increases the chances that other users will engage the question and reach a "leave open" verdict).
Is there precedent for other sites doing this?
Yes. After the SO experiment, Hardware Recommendations.SE ran one of their own. They had similar results, and ultimately lowered their threshold to one vote. That's a bit extreme for us, but Hardware Recs gets a high volume of questions, so being able to clean those up faster was a priority.
Let us know if you like this idea -- a simple up or down vote will suffice, or feel free to opine in an answer.
We'll wait until 12 June 2020 (two weeks from today) to allow plenty of time for feedback. At that point, we'll then escalate this question to the Stack Exchange community management team (using the new process started in March) to implement the change.