Sampling is the process researchers use to determine whoshould participate in their study. A sample should be representative ofthe population. For example, TV shows are rated by the Nielsen company. Nielsen does not check out every home in America (the population) to see whatpeople are watching. Rather, a sample of American homes is selected torepresent the entire population. In order for the Nielsen ratings to reallyreflect America's TV viewing habits, all types of Americans must be representedin the sample, and in the same proportion that they exist in the population. Choosing Nielsen families from a list of credit card holders, for example,automatically excludes all people who do not have credit cards, and is notrepresentative of the population.

Sample size is an important factor in statistics. The larger thesample size, the more likely it is that the results are reliable. A smallsample size is an indicator that the results may not apply to the population asthe experimenter intended.

A sample should also be drawn at random, to avoid any intentional orunintentional bias in choosing the subjects. A random sample means that eachperson in the population has an equal chance of being chosen for participationin the sample.