Simple Random Sampling
This is simplest and most popular technique of sampling. In it each unit of the population has equal chance of being included in the sample. This method impels that if N is the size of the population and n units are to be drawn in the sample then the sample should be taken in such a way that each of the N _{Cn} sample has an equal chance of being selected.
Simple random sampling gives
a. Each element in the population an equal chance of being included in the sample and all choices are independent of each other.
b. Each possible combination an equal chance of being chosen.
The method of simple random sampling eliminates the chance of bias or personal prejudices in the selection of units. Some of the common method of drawing simple random samples are (a) lottery method (b) Random Sampling number.
Lottery Methods : The followings are the steps in this methods. Let N be the size of population and a sample of size n is to be drawn.
- Number the units of the population from 1 to 2.
- Take N identical pieces of papers cards capsules or balls and number these from 1 to N.
- Mix these thoroughly in a bag bowl or some other container and pick out n items either one by one or in one stroke blind folded.
- The number of units in the population bearing the numbers on the items drawn in step will constitute the desired random sample.
By Using Random Number A number of people viz.... . L. H. C. Tippet fisher and Yates Kendall and smith Oliver and Boyd and rand corporation constructed set of random number. These numbers can be sued to select random samples from a given population. A table of true random numbers is one in which any digit from 0 to 9 have an equal chance of appearing in any position of the table. Random numbers are most useful when population is of infinite size. The digits in random number tables are selected at random and are arranged independently of digits occupying other places in a number. The random number table prepared by L.H. C. Tippet contains a set of 10400 four figure numbers.
Advantages of Simple Random Sampling :
a. The method is objective .
b.The conclusions can be derived in terms of probability or errors of estimation.
c. Accurate mathematical tests may be applied to judge the randomness of the sampling .