A collection of elements drawn in such a way is referred to as a probability sample. The first condition imparts a degree of objectivity to a probability sample and, in combination with the other two conditions, secures a basis for statistical inferences concerning descriptive parameters of the population.
Random Sampling
In random sampling, the sample is drawn according to prespecified chances from the population, and thus it is also called probability sampling. Since planned randomness is built into the sampling design according to the probabilities, one can use these probabilities to make inferences about the population.