RedditDiscovery6 min readRanking a crowd against itself
Two arrows, a time decay, and a sort menu that changes the site.
- The surface
- The subreddit and home listings, the vote arrows on posts and comments, and the sort controls including Hot, New, Top and comment sorts.
- What the user wants
- I want to see what is worth reading in this community right now, without wading through the rest.
Two arrows
Every post and comment carries an up and a down vote, available inline without opening anything.
Binary judgement at minimal cost
A five point scale asks people to calibrate, which is work and produces noisy results. A binary choice can be made in the time it takes to read a title, so participation is wide enough to be meaningful. A downvote also exists, which most platforms avoid, and it is what lets a listing actively bury things.
Time decay in the default sort
The default listing weighs score against submission age, so older posts fall even as their score rises.
Recency-weighted ranking
Pure score ranking freezes: the top post keeps accruing votes because it is on top, and nothing new can ever compete. Decay forces turnover, which is what makes a returning visitor find a different page. The ranking is designed to keep a market for attention open rather than to be correct.
The sort menu
Users can switch the same listing to New, Top over a chosen period, Rising, or Controversial.
Explicit control over the algorithm
Different jobs need different orderings, and no single ranking serves the person catching up, the person moderating and the person looking for the best of the year. Exposing the sort rather than inferring it treats the user as capable. It also makes the ranking legible, which is rare.
Comment sorting separately
Comment threads have their own sort, with Best as a default and Q&A, New and Controversial available, and threads are nested.
Separating two different ranking problems
A good post and a good comment are judged on different things, and a comment's value often depends on what it replies to. Nesting preserves that dependency, and a separate sort stops a slow, thoughtful reply from being invisible under an early joke. Most products reuse one ranking for both and lose the distinction.
Subreddits as the unit
Communities are separate spaces with their own rules, moderators and norms, and voting happens inside that context.
Contextual norms
What counts as a good post is not a global property, and a single site-wide feed would average incompatible standards into mush. Scoping the vote to a community lets each one define quality for itself. The moderation labour that makes this work is unpaid, which is the arrangement's real fragility.
Vote fuzzing and hidden scores
Displayed scores are approximate, and new comment scores are hidden for an initial period.
Breaking the information cascade
If early voters see a score, they tend to follow it, and the first few votes decide the outcome. Hiding the number for a window forces independent judgement while the ranking is still forming. Fuzzing separately makes vote manipulation harder to measure and therefore harder to sell.
Making the ranking arguable
What not to copy
- Early votes still dominate despite fuzzing. A post's fate is largely set in the first minutes, which rewards timing and coordinated voting over quality.
- Downvoting is nominally for irrelevance and is used for disagreement, which pushes minority positions out of visibility and makes threads more homogeneous than the community actually is.
- The whole quality system rests on volunteer moderators with real power and no support, and the platform has repeatedly discovered how load-bearing that is only during disputes.
- Controversial sort and decay together favour posts that provoke fast reaction, so the default page systematically overrepresents whatever is easiest to have an opinion about.
The takeaway
Expose the sort. Letting users choose the ranking is cheaper than guessing their intent and makes your system arguable instead of mysterious.
Finished the teardown? Bank it and the day counts toward your run.
Where the principles come from
- Influence: The Psychology of Persuasion (social proof), Robert Cialdini
- Governing the Commons, Elinor Ostrom
- The Wisdom of Crowds, James Surowiecki
- Information cascades and herding, Sushil Bikhchandani, David Hirshleifer and Ivo Welch
Written from public behaviour of the product, not from inside it. Interfaces change often, so treat the flow described here as of the time of writing and check the live product before quoting it.