operating-systems on S Anand

Visualising the Wilson score for ratings

Wed, 24 Nov 2010 10:48:13 +0000

Reddit’s new comment sorting system (charmingly explained by Randall Munroe) uses what’s called a Wilson score confidence interval.

I’ll wait here while you read those articles. If you ever want to implement user-ratings, you need to read them.

The summary is: don’t use average rating. Use something else, which in this case, is the Wilson score, which says that if you got 3 negative ratings and no positive ratings, your average rating shouldn’t be zero. Rather, you can be 95% sure that it’ll end up at 0.47 or above, given a chance, so rate it as 0.47.

I understand this stuff better visually, so I tried to see what the rating would be for various positive and negative scores. Here’s the plot.

The axes on the floor show the number of positive and negative ratings (you can figure out which is which), and the height of the surface is the average rating it should get.

You can see that if there are only positive ratings, the average rating is 100% (because there’s a 95% chance it’ll end up at 100% or above). If there are only negative ratings, the rating falls of sharply. In the early stages, a few positive ratings can correct that very quickly, but over time, the correction’s a lot weaker.

You can move your mouse over the visualisation to control the angle. (For those reading this this via the RSS feed, you may need to visit my blog.) Try it out: I understood the behaviour a lot better this way.

Comments

Safe Hammad 8 Dec 2010 5:49 pm: Very interesting! Great visualisation. Although using the Wilson score confidence interval is “more correct” than simpler alternatives, I can’t help feel that web sites need absolute transparency as much as correctness when it comes to how their rating system works. I wonder what would happen if Amazon or Urban Dictionary had to point visitors to Wilson’s formula to help them understand how their ratings system worked! There may be a case for the trade-off between simplicity and correctness. Thankfully many sites, including both Amazon and Urban Dictionary, also publish the raw data i.e. a breakdown of ratings allowing visitors to draw their own conclusions … should they choose to do so.
Dan Murray 22 Dec 2010 6:22 pm: I don’t like the 3D representation. It obscures the meaning.

Ubuntu 8.10 on a Dell Latitude D420

Thu, 15 Jan 2009 12:00:00 +0000

Here’s the fastest way I’ve found to install Ubuntu on a USB flash drive, for my Dell Latitude D420. (Pendrivelinux.com is a great resource for this sort of thing.)

Ingredients

One large USB flash drive like this one. Not less than 4GB. I’d suggest 8GB or more
One CD (not a DVD)
Ubuntu 8.10 desktop CD ISO
IMGBurn or any other CD burning software
Direct Internet via LAN cable (without proxy, without wireless)

Installation

Burn the Ubuntu ISO file on the CD
Press F12 when the laptop boots up, and select CD/DVD Drive as the boot device
On the Ubuntu splash screen, select “Try Ubuntu without making any change to your computer” and wait
Insert the flash drive
Go to System > Administration > Create a USB startup disk and follow instructions there
Once done, remove the CD and reboot using the USB flash drive (pressing F12 during the boot sequence)

To enable wireless, which won’t work by default

Connect to the Internet using a LAN cable
Go to System > Administration > Hardware devices
Select the Broadcom LAN driver, and activate it

That’s it. It’s been a fairly painless installation.

I do have one big crib. I planned to use Hibernation (or suspend-to-disk on Ubuntu) to switch between Windows and Ubuntu. But there are a couple of problems:

Hibernate doesn’t work on Ubuntu. I need to reboot Ubuntu every time, and that takes 3 minutes
When Windows is hibernating, Ubuntu can’t access any files on the hard disk

This means switching between Ubuntu and Windows is roughly a 6 minute shutdown-one-OS-reboot-the-other process rather than the 1-minute hibernate-one-OS-resume-the-other that I had had hoped for.

Another minor problem I have is that our Exchange server doesn’t seem to have an IMAP interface, at least that I know of. So I can’t check mail. But like I said, it’s minor. I just forward mails from my BlackBerry to GMail.

Comments

deeaycee 19 Jan 2009 10:50 am: Your post is how I got my wireless working. Thank you.
I’m also using a Dell D420. I have 8.10 on a 8g Attache flash drive. I ran into a problem while updating. I’m stuck at kernel 2.6.27-7 and it should be updating to 2.6.27-11. The error it gives has something to do with running from a live-cd. After some research, I found that there is a bug that prevents solid updates from the live-cd. The work-around is to actually do a real install to the flash drive from the live-cd. This presents another problem/bug. The only way to see the flash drive during the install is to disconnect the hd, so the install prg doesn’t see it. It was suggested to physically disconnect the hd, but I wonder if it could be done temporarily through the bios. I’ll try this later today. I haven’t even thought about the hibernation/suspend issues yet. Good luck!
ActionParsnip 30 May 2010 10:22 pm: orks 100% OOTB with Ubuntu Lucid.