Since it is also considered as answer in one of the mcqs along with 'probability theory'
What do you mean how? Is it the logical reasoning behind random selection of items, you are questioning or do you want to know how random selection is done. Statistical sampling should ensure (i) The sample items should have a known probability of selection- for example, by random selection. (ii) The sample results should be evaluated mathematically â?? that is, in accordance with probability theory Random selection allows every item to be part of selection