SIMPLE RANDOM SAMPLING

Random sampling is one popular and extensively used sampling method In this method, each and every unit of the population has an equal chance of being selected or included in the sample Random selection does not mean haphazard selection It is one type of selection in which every item in the universe has an equal chance of being selected alone with all other items In random sampling, the complete list of the universe is taken but the selection is made ‘at random’ from this list However, some uniform system is used for the selection of sample Random sampling is useful for the conduct of telephone or mail survey It is an ideal method in the surveys of specialized nature

The process of randomness does not mean that it is ‘haphazard’, as a layman may be inclined to think. What it means is that the process of selecting a sample is independent of human judgment. To ensure this, there are two methods that are followed when drawing a random sample. These are:(i)the lottery method and (ii)the use of random numbers.

In the lottery method, each unit of the population is numbered and shown on a chit of paper or disc. The chits are folded and put in a box from which a sample of the requisite size is to be drawn. In case discs are used, these are well mixed up before a draw is made so that no particular unit can be identified before it gets selected. The sample is drawn in the same manner as winning numbers in a lottery are drawn

In the second method, the tables of random numbers are used. The members of the population are numbered from 1 to N from which n members are selected. This process is explained below with the help of an illustration.

Suppose a sample of size 50 is to be selected from a population of 500. First, number the 500 units from 1 to 500, the order being quite immaterial. While numbering the units, ensure that each unit in the population has uniform digits, in this case, three. Thus, 1st unit would have a three-digit number 001, 2nd unit 002, 10th unit 010, 11th unit O11, and so on. After the units have been given three-digit numbers, the table of random numbers is to be used. One may start from the left-hand top corner of the table of random numbers and proceed systematically down sets of three-digit columns, rejecting numbers over 500 and those that have occurred earlier.

Using the first thousand numbers from the table of random numbers (an excerpt from the table is given below), a sample of 50 out of 500 will thus be chosen.

231 055 148 389 117 433 495 367 070 313

092 259 113 455 126 426 062 401 100 488

434 325 211 207 398 225 485 035 171 047

318 263 239 108 379 420 122 441 493 310

032 194 144 337 224 006 068 043 500 222

Advantages Of Simple Random Sampling Method

(1) Simplicity: Simple random sampling issimplest method of probability sampling and can be used for different types of surveys

(2) Scientific: This method isscientific as there is equal opportunity to every unit for selection as sample

(3) Truly representative character: The samples selected by this method aretruly representative in character.

(4) Quality results: Random sampling can beused effectively (for quality results) when the universe to be studied is small and can be listed accurately (e. g. motor car owners in a city)

 Limitations Of Simple Random Sampling Method

(1) Difficult when the universe is very large: In simple random sampling, the whole list of universe is taken up for selection Obtaining the complete and up-to-date list of the universe is difficult It is difficult particularly when the universe is very large in number.

(2) Costly: The cost for conducting survey by this sampling method is high as the samples are selected at random and it is obligatory to contact them and collect the information

(3) May prove inefficient: This methodmay prove to be statisticallyinefficient and provide a larger standard of error than the other types of sampling designs

(4) Administrative   difficulties: Random samplinginvolves administrative difficulties as regards the selection of sample and follow-up measures for the collection of information

(5) May not be fully represented: The sample selectedmay not befully representative as the selection is from the whole population and not from the groups that constitute the population