# Probability sampling

Probability sampling is a selection of elements from the total population for a statistical sample, in which all elements have the same and known probability of being selectedIf this condition is not met then the selection of elements (sampling) is considered as a non-probability sampling.The non-probability sampling is a method that does not even give some elements in a sampling a chance to be in it.

The main rules of probability sampling are:

• knowledge of number of the whole population when a sample is selected
• knowledge of the probability of selecting each of the elements

The "nonzero" definition in probability sampling says that each element in the population should have a higher chance of getting into the sample - at least more than 0%. The non-probability sampling is a method that does not even give some elements in a sampling a chance to be in it. In population studies, it is very important to choose an appropriate sampling method because each has its own advantages and disadvantages. Some people try to combine the two methods together .