Simple random sampling - sampling decisions, Operation Research

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 .

 

 

Posted Date: 2/26/2013 4:35:17 AM | Location : United States







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