Researchers usually draw conclusions about large groups by taking a sample
A Sample is a segment of the population selected to represent the population as a
Ideally, the sample should be representative and allow the researcher to make accurate
estimates of the thoughts and behaviour of the larger population.
Designing the sample calls for three decisions:
Who will be surveyed? ( The Sample)
•  The researcher must determine what type of information is needed and who is most
likely to have it.
How many people will be surveyed? (Sample Size)
•  Large samples give more reliable results than small samples. However it is not necessary to sample the entire target population.
How should the sample be chosen? (Sampling)
•  Sample members may be chosen at random from the entire population   
        ( probability sample)
•  The researcher might select people who are easier to obtain information from
   ( nonprobability sample)
·        The needs of the research project will determine which method is most effective