Probability sampling is a method for selecting choices on a completely random basis. Commonly, probability sampling is used to ensure that the selected sample is totally random, and not subject to any controls or rigging. This system works well, as long as all rules are followed, and the system is not violated in any way.

The principal advantage of probability sampling is fairness, as in contests where names are selected from a box full of entry forms. A selector will reach into the box, without looking, and pluck out the winner's name. This sort of selection process guarantees that every entrant has an equal chance at winning a prize.

The disadvantage of probability sampling is the possibility of flaws to the randomness model - in other words, people may cheat the system or interfere with the innate fairness of the probability sampling system. For example, in a contest, illegal or duplicate ballots may be added to a box, weighting the odds in someone's favor.

Today, many probability sampling exercises are used along with electronic devices (computers are a popular choice for performing probability sampling).

An example of probability sampling would include an Internet contest on Facebook, where people will "like" a company or person's Facebook page and be automatically entered into a contest. When the contest end date arrives, the Facebook page administrator will select a winner at random from all entrants. This may be accomplished through random generation software that guarantees a fair result.

In lieu of software, a person may simply close their eyes and point at a list of name, and then choose the winner whose name is closest to their finger. This type of sampling can be low or high tech. Probability sampling only works when all people participating in a sampling event respect the integrity of the entire process.
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