A/B tests with Google Events -- see http://huffpostdata.tumblr.com/post/55003907576/simple-a-b-tests-with-google-events

abtest.js

/*

  Usage:

  When generating a page:
    var abTest = new AbTest('your-test-slug');

    if (abTest.variation == 0)
      $('#thediv').addClass('red');
    else if (abTest.variation == 1)
      $('#thediv').addClass('blue');

  When the goal is reached/passed:
    $("#thediv").click(function() {
       abTest.pass();
    });

  slug: A unique identifier for your AbTest
  numVariations: The number of variations your test has (2 by default)

*/
function AbTest (slug, numVariations) {

  this.load = function() {
    if (!this.runnable || this.loaded) return;
    this.loaded = true;
    _gaq.push(['_trackEvent', 'abtest', this.slug, 'load-' + this.variation]);
  }

  this.pass = function(value) {
    if (!this.runnable || this.passed) return;
    this.passed = true;
    _gaq.push(['_trackEvent', 'abtest', this.slug, 'pass-' + this.variation, value, true]);
  }

  this.setVariation = function() {
    var variationKey = "abtest-" + this.slug;
    if (!this.runnable) return;

    var pVariation = this.paramVariation();
    if (pVariation) {
      this.variation = parseInt(pVariation);
      return;
    }

    if (localStorage.getItem(variationKey) === null)
      localStorage.setItem(variationKey, Math.floor(Math.random()*this.numVariations));
    this.variation = parseInt(localStorage.getItem(variationKey));
  }

  this.paramVariation = function() {
    var params = window.location.search.substr(1).split('&');
    for (var i = 0; i < params.length; i++) {
      var p = params[i].split('=');
      if (p.length == 2 && p[0] == this.slug)
        return p[1];
    }
    return null;
  }

  this.slug = slug;
  this.numVariations = typeof(numVariations) !== 'undefined' ? numVariations : 2;
  this.variation = 0;
  this.runnable = (_gaq && typeof(localStorage) !== 'undefined');
  this.loaded = false;
  this.passed = false;

  this.setVariation();
  this.load();
}