We calculate your accuracy score by looking at how many trades you made in the "right direction," then held them until the question ended. For example, let's say you bought shares (said the chances or value should be higher) for the Chicago Bears to win the Super Bowl and held them until the game was played. The Bears then win. We would add that result to your total accuracy percentage. The percentage is calculated by dividing the number of questions you traded correctly by the total number of questions you held positions in at the end.
Similarly, we perform this same calculation for individual topics and tags to see what topics you've seen the most success in.
You earn karma by doing things that help the site community like answering the free polls. Soon there will be other ways to earn karma like having people vote up comments you make about a question, closing out a question promptly, and getting a question published.
How are worth and the leader board calculated?
The leader board is refreshed multiple times per day and uses your total worth: the sum of your "current holdings" + "total cash." Your current holdings is what your positions are currently worth if you were to get out of them at this moment. Your total cash is money you've made from previous transactions (or that was granted to you) that is not currently being used.