Consider an experiment that can result in M possible outcomes, O ₁, , O _M. For example, in tossing a die, one of the six sides will land facing up. We could let O _i denote the outcome that the ith side faces up, i = 1, , 6. Alternatively, we might have a computer with six processors, and O _i could denote the outcome that a program or thread is assigned to the ith processor. As another example, there are M = 52 possible outcomes if we draw one card from a deck of playing cards. Similarly, there are M = 52 outcomes if we ask which week during the next year the stock market will go up the most. The simplest example we consider is the flipping of a coin. In this case there are two possible outcomes, heads and tails. Similarly, there are two outcomes when we ask whether or not a bit was correctly received over a digital communication system. No matter what the experiment, suppose we perform it n times and make a note of how many times each outcome occurred. Each performance of the experiment is called a trial. ^[b] Let N _n( O _i) denote the number of times O _i occurred in n trials. The relative frequency of outcome O _i,

is the fraction of times O _i