Biased. Even in this era, does everyone have a phone? What types of persons might not have phones? Do some phones have unlisted numbers? What persons are likely to have unlisted numbers?
The type of sampling described here is known as random sampling. Random sampling involves selecting individuals from a population in such a way that each individual has an equal chance of being chosen. In this case, telephone numbers were randomly generated by a computer, ensuring that each individual had an equal opportunity to be included in the Gallup poll.
