I think this should be "never downvote".
Seems to me that a downvote would associate negative valance with both the act of posting on LW and with whatever their specific mistake is, with the latter being stronger. So no vote and a comment with a mixture of praise and criticism is probably the stronger play if you're looking to improve someone's writing or fix some technical mistake while keeping them as a contributor, but a downvote is still effective if all you care about is seeing fewer posts of that kind.
Part of the sequence: The Science of Winning at Life
Also see: Basics of Animal Reinforcement, Basics of Human Reinforcement, Physical and Mental Behavior, Wanting vs. Liking Revisited, Approving reinforces low-effort behaviors, Applying Behavioral Psychology on Myself.
Story 1:
On Skype with Eliezer, I said: "Eliezer, you've been unusually pleasant these past three weeks. I'm really happy to see that, and moreover, it increases my probability than an Eliezer-led FAI research team will work. What caused this change, do you think?"
Eliezer replied: "Well, three weeks ago I was working with Anna and Alicorn, and every time I said something nice they fed me an M&M."
Story 2:
I once witnessed a worker who hated keeping a work log because it was only used "against" him. His supervisor would call to say "Why did you spend so much time on that?" or "Why isn't this done yet?" but never "I saw you handled X, great job!" Not surprisingly, he often "forgot" to fill out his worklog.
Ever since I got everyone at the Singularity Institute to keep work logs, I've tried to avoid connections between "concerned" feedback and staff work logs, and instead take time to comment positively on things I see in those work logs.
Story 3:
Chatting with Eliezer, I said, "Eliezer, I get the sense that I've inadvertently caused you to be slightly averse to talking to me. Maybe because we disagree on so many things, or something?"
Eliezer's reply was: "No, it's much simpler. Our conversations usually run longer than our previously set deadline, so whenever I finish talking with you I feel drained and slightly cranky."
Now I finish our conversations on time.
Story 4:
A major Singularity Institute donor recently said to me: "By the way, I decided that every time I donate to the Singularity Institute, I'll set aside an additional 5% for myself to do fun things with, as a motivation to donate."
The power of reinforcement
It's amazing to me how consistently we fail to take advantage of the power of reinforcement.
Maybe it's because behaviorist techniques like reinforcement feel like they don't respect human agency enough. But if you aren't treating humans more like animals than most people are, then you're modeling humans poorly.
You are not an agenty homunculus "corrupted" by heuristics and biases. You just are heuristics and biases. And you respond to reinforcement, because most of your motivation systems still work like the motivation systems of other animals.
A quick reminder of what you learned in high school
What works
Example applications
For additional examples and studies, see The Power of Reinforcement (2004), Don't Shoot the Dog (2006), and Learning and Behavior (2008).
I close with Story 5, from Amy Sutherland:
Next post: Rational Romantic Relationships Part 1
Previous post: The Good News of Situationist Psychology
My thanks to Erica Edelman for doing much of the research for this post.