Some OR-Exchange stats

OR-Exchange is a question-and-answer site for Operations Research, along the same lines as Stack Overflow for programming, but smaller and less strict. If you don’t know what Operations Research is, then OR-Exchange won’t be a place you’ll want to visit. If you do, then check it out, it is a useful place to get answers to OR questions and discuss OR topics.

I recently downloaded some of the data from the site, specifically the user reputation information. If you go to a user’s karma history page (here is mine) you see a little graph plotting karma over time. The HTML source contains the coordinates for each point, and I extracted all of these, for all users, into a dataset.

A user’s karma changes when someone votes on one of his questions or answers, or when he votes down someone else’s. It can be considered a proxy for activity on the site, although it doesn’t capture all activities. The rest of this post explores some basic analysis on this reputation data. In a later post I will extend this analysis to data about questions and answers themselves.

Please note that I am not trying to put undue attention on karma. I don’t want OR-Exchange to turn into a place that is gamed to accumulate karma, or where high karma implies you are a better person. This is just the first set of data I’ve extracted, and it is fun to examine.

General site activity

The site was started in November 2009 by Mike Trick, so we are coming up on its third anniversary. If we count the number of users that were active (had some karma activity) in each month since, we get the following graph.

It looks like there hasn’t been substatial growth in the number of active users for quite a while. However, these are users that get karma points, in any question-and-answer site, there will be many more people who view and vote on questions than those who answer them, and this is still valid activity. I don’t have data on page views, but we can graph the combined points accrued each month, which will capture those who vote.

Again, we see that site activity has fluctuated around the same levels since early 2010.

If we consider an event to be any occurence of a user’s reputation changing, the following graph shows on which day of the week people are voting on the site.

We can also plot the time of day that karma events occur.¹

User karma

Of all the registered users on the site, few of us have accumulated lots of karma points, but a decent number have accumulated several hundred points. The graph below shows the distribution.

There are 14 users with more than 1000 karma points and the graph below shows the accumulation of points for these users since the site began.

Note that the user with the most karma, Paul Rubin, is well ahead of everyone else. It is also interesting to consider how fast users accumulate karma after joining. The following graph shows the karma accumulation for the firstt 500 days after joining for users with more than 1000 points.

I’ve calculated some “awards” for arbitrary karma-based records and milestones.

Most points in a single day:

Place	Name	Points	Date
1st	Matthew Saltzman	180	09Apr2011
2nd	Paul Rubin	140	19Apr2010
3rd	David Woods	120	22Apr2010
4th	Marco Lübbecke	110	16Feb2012
5th	Marco Lübbecke	110	10Sep2012

Worst single day:

Place	Name	Points	Date
1st	Mark	-50	01Jan2010
2nd	Jessy	-41	19Feb2012
3rd	Mark	-25	03Dec2009

Most points in a month:

Place	Name	Points	Month
1st	David Woods	582	Jun2010
2nd	Larry	502	Apr2010
3rd	Paul Rubin	495	Apr2010
4th	Marco Lübbecke	444	Jan2012
5th	Geoffrey De Smet	426	Jul2012

Best first week after joining:

Place	Name	Points
1st	David Woods	358
2nd	Bjarni Kristjansson	196
3rd	Michael Trick	95
4th	Geoffrey De Smet	93
5th eq	Mark & Ahmet Yukselturk	91

Best first 30 days after joining:

Place	Name	Points
1st	David Woods	498
2nd	Marco Lübbecke	360
3rd	Michael Trick	325
4th	Mark	310
5th	Bjarni Kristjansson	306

Highest points rate since joining:

Place	Name	Join date	Karma	Days	Points per day
1st	Paul Rubin	19Nov2009	7083	1034	6.85
2nd	Marco Lübbecke	17Dec2011	1776	276	6.43
3rd	Ng Yee Sian	01Jul2012	416	79	5.27
4th	jfpuget	09Jun2012	416	101	4.73
5th	David Woods	19Apr2010	3867	883	4.38

And finally, for the record, the 14 users who at the time of data extraction had over 1000 karma points are: Paul Rubin (7083), David Woods (3867), Bo Jensen (3584), Michael Trick (3462), Mark (3460), Larry (2957), Matthew Saltzman (2454), Florian Bahr (2175), Geoffrey De Smet (2068), Ehsan Nikbakhsh (2035), Tallys Yunes (1803), Marco Lübbecke (1776), Gilead (1604), and Samik R. (1009).

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1. The time values on the site seem to be UTC. I’ve aligned these to the time that is displayed against events on the site itself, for me. I haven’t looked at whether this is local Melbourne time or something else. ↩