CHAPTER 6: SAMPLING DESIGNS

Sampling – may be defined as the method of getting a representative portion of the population.
Population –is the aggregate or total of objects, persons, families, species, or orders of plants or animals.
Advantages of Sampling
1.      It saves time, money and effort.
2.      It is more effective.
3.      It is faster, cheaper and economical.
4.      It is more accurate.
5.      It gives more comprehensive information.
Disadvantages of Sampling
1.      Sample data involve more care in preparing detailed sub classification due to small number of subjects.
2.      If the sampling plan is not correctly designed and followed, the results may be misleading.
3.      Sampling requires an expert to conduct the study in an area. If this is lacking, the results can be erroneous.
4.      The characteristic to be observed may occur rarely in a population.
5.      Complicated sampling plans are laborious to prepare.
Planning a Sample Survey
1.      State the objectives of the survey.
2.      Define the population.
3.      Select the sampling individual.
4.      Locate and select the source list of particular individuals to be included in the sample.
5.      Design the sampling design to be used that suits to the study, either scientific or nonscientific sampling.
6.      Determine the sample size.
7.      Select the method in estimating the reliability of the sample.
8.      Test the reliability of the sample in a pilot institution.
9.      Interpret the reliability of the sample.
10.  Choose experts to administer the research instruments.
Determination of Sample Size
Step 1: Determine the total population (N) as assumed subjects of the study.
Step 2: Get the value of V(2.58), Se(0.01), and p(0.50).
Step 3: Compute the sample size using this formula:

Ss = NV + [ Se2 (1-p)]
NSe + [ V2p(1-p)]
Sampling Designs
Scientific Sampling
1.      Restricted random sampling – This type of sampling design involves certain restrictions to improve the validity of the sample.
2.      Unrestricted random sampling – This is the best random sampling design due to no restrictions imposed, and every member in the population has an equal chance of inclusion in the sample.

• Lottery Technique
• Table of Random Numbers

3.      Stratified random sampling – This type of design divides the population into two or more strata.
4.      Systematic sampling – In this type of design the individuals of the population are arranged in a methodical manner.
5.      Multistage sampling – This design is done in several stages.
6.      Cluster sampling – In this type of design, the population is grouped into clusters or small units.
Nonscientific sampling
1.      Purposive sampling – This type of nonscientific sampling is based on selecting the individuals as samples according to the purpose of the researcher as his controls.
2.      Incidental sampling – This type of sampling design is “applied to those samples which are taken because they are the most available.”
3.      Quota sampling – This type of design is popular in the field of opinion research because it is done by merely looking for individuals with the requisite characteristics.