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Showing posts from 2009

Baye's Theorem: Cut it out!

There is this big crowd of people who are desperately trying to to be a part of community that knows the answer to: "Why did that Bayesian traveler didn't crossed the road?" To them it looks like the world is divide into two parts: Smart-ass people who knows what Bayes is all about; and they themselves! To all my friends on the other side, here's a chance to grasp Bayes in most intuitive way (I assume you know basic probability stuff)! The Problem: (Courtesy: http://yudkowsky.net/rational/bayes) 1% of women at age forty who participate in routine screening have breast cancer. 80% of women with breast cancer will get positive mammographies. 9.6% of women without breast cancer will also get positive mammographies. A woman in this age group had a positive mammography in a routine screening. What is the probability that she actually has breast cancer? Variables: Lets assign the good old variables to the events we have in the problem: A: People with cancer B: People wi...

Efficient Captchas

There is a whole lot of buzz in the internet about alternatives to captchas (i mean alternatives to image captchas). Its not mainly because captchas are not secure against bots, but because they aren't convenient!!! People are getting bugged because of highly illegible captcha strings (http://tinyurl.com/5bvk7c). But i really feel, captchas, if done properly are the best form of human recognition technique. Its simple, fast, and sufficiently secure. People are used to image captchas, and it just works! I get more bugged when I'm asked silly questions, or to solve a mathematical equation or when i have to select kittens out of 9 pictures of animals!!! I put up some points here on how to create usable and convenient captchas: 1. Use a light background. I'll prefer a plain white background. Backgrounds do provide some security but having a regular background for all captchas does not helps as an average captcha solving algo will adapt itself to it. So, its always better to pre...