Random Sampling Method
In this method the units are selected in such a way that every item in the whole universe has an equal chance of being included. In the words of croxton and Cowden. Sampling is said to be random if each possible sample had the same probability of being drawn. Simpson Kafka said, A random sample is a sample is a where each item in the universe has an equal or known opportunity of being selected.
Thu s if the size of sample is n from a finite universe of size N. The there are possible sample .A sampling technique in which each of the sample has an equal chance of being selected is known as random sample.
Method of Random Sampling: To ensure randomness of selection one may adopt either of the following methods;
(1) Lottery Method: Under this method all items of the population are numbered on separate slips of paper of identical size and shape .There slips are folded and mixed up in a drum .A blind fold selection is then made of the required number of sample size, the method is common in lottery draws where a decision for the prizes is to be made.
(2) By Rotating Drum or Machine: In this method a machine or a drum is used, In this machine there are some discs on which numbers from 0 to9 are graved, The number of discs will depend upon the units of the population. If the total numbers in the universe is up to 999 three discs are required. If the number is from 1000 to9999 four discs will be needed. For every disc there is an index sing marked on it which identifies thedigit. all the discs are rotated and left. Wherever the discs are stopped the numbers are noted. In this manner desired units are selected.
(3) By Random Numbers :The random numbers are usually obtained by some mechanism which, when repeated a large numbers of items, ensures equal frequencies for the numbers from 0 to9 and also proper frequencies for various combinations such as 00, 01,99,000,001,999, etc. That may be expected in a random sequence of digits 0 to 9.