Reasons to Keep a Blog and How to Get Beta Users

Number one, if you like to write and I do, then it’s fun. But as Steve Yegge outlines in his post “You Should Write Blogs” it’s also good for you. I won’t repeat Steve’s points but I do want to add one point and that is a blog is a very easy way to keep track of little tidbits of information that could otherwise be hard to refind. As an example all my posts on mono, nginx, asp.net, and asp.net mvc were written purely because I did not want have to try and find the information again or try and dredge it up from my poor memory. Instead I wrote the posts and now whenever I need to reconfigure a server to use nginx with mono and asp.net I can easily find the information on my blog. In a way it’s an extension of your memory, it’s a permanent easily searchable record of what you have done.

In that spirit I’m linking to Patrick Swieskowski and Sascha Kuzins’ post, How we got 18,000 beta users in 4 weeks. Now when I need to look up how to get beta users I can simply search my blog and find this article.

Statistically Accurate Ratings

In a previous post on ratings I noted some issues with using the mean vs the media for the rating. A few days ago Jeff Atwood posted on user ratings and specifically how to sort a set of items that are rated by users. Jeff’s post included material from Evan Miller’s article, How Not To Sort By Average Rating, on the same subject.

Below is the relevant portion of Evan Miller’s article:

CORRECT SOLUTION: Score = Lower bound of Wilson score confidence interval for a Bernoulli parameter

Say what: We need to balance the proportion of positive ratings with the uncertainty of a small number of observations. Fortunately, the math for this was worked out in 1927 by Edwin B. Wilson. What we want to ask is: Given the ratings I have, there is a 95% chance that the “real” fraction of positive ratings is at least what? Wilson gives the answer. Considering only positive and negative ratings (i.e. not a 5-star scale), the lower bound on the proportion of positive ratings is given by:

wilson confidence interval formula

(For a lower bound use minus where it says plus/minus.) Here p is the observed fraction of positive ratings, zα/2 is the (1-α/2) quantile of the standard normal distribution, and n is the total number of ratings. The same formula implemented in Ruby:

require ‘statistics2’

def ci_lower_bound(pos, n, power)
if n == 0
return 0
end
z = Statistics2.pnormaldist(1-power/2)
phat = 1.0*pos/n
(phat + z*z/(2*n) – z * Math.sqrt((phat*(1-phat)+z*z/(4*n))/n))/(1+z*z/n)
end

pos is the number of positive rating, n is the total number of ratings, and power refers to the statistical power: pick 0.10 to have a 95% chance that your lower bound is correct, 0.05 to have a 97.5% chance, etc.

Now for any item that has a bunch of positive and negative ratings, use that function to arrive at a score appropriate for sorting on, and be confident that you are using a good algorithm for doing so.

Sadly everybody has simply quoted the mathematical forumla and not even given links to the material on how to derive the formula. I was able to find an article by Keith Dunnigan here that gave an outline of how it is derived along with several other confidence intervals. Hopefully later I can take a look at my textbooks and do a full derivation.

How To Auto-login Using ASP.Net FormsAuthentication

For our demo website, demo.quickpm.net, I need to have a default automatic login. Using the ASP.Net Membership and FormsAuthentication an easy way to do auto-login is the following code

string userEmail = "john.doe@gmail.com";
string password = "thepassword";
if (Membership.ValidateUser(userEmail, password))
{
      FormsAuthentication.SetAuthCookie(userEmail, true);
      Response.Redirect("~/");
}

The above code assumes that “john.doe@gmail.com” is a user and “thepassword” is their password.

Mono Asp.Net MVC and Nginx

I’ve been using Mono ASP.Net for a while with Nginx as the server. I recently started playing around with ASP.Net MVC and discovered that it doesn’t play nice when using Nginx as the server. To make ASP.Net work with Mono and Nginx you need to download the Mono source from here. And then modify the file mcs/class/System.Web.Routing/System.Web.Routing/Route.cs
in particular comment out the following lines in the GetRouteData function

if (pathInfo != String.Empty)
throw new NotImplementedException();

If you comment out the above two lines your MVC website should work just fine when hosting it using Mono and Nginx. I don’t know if there are any negative consequences for commenting out the above two lines but I have not encountered any.