Sampling is examining by taking a sample -a part representing the whole (population).
Types of Sampling
Random Sampling
Selection of members of a group haphazardly where every item has an equal chance of being selected e.g. to select 5 students to go for a tour from a class:
- Class members write their names on pieces of paper
- They are folded and put in a basket
- The basket is shaken and fives papers are taken out
Systematic Sampling
Selection of members of a sample from an evenly distributed phenomena at regular intervals e.g. after every 10 items/members.
Stratified sampling
Selection of members of a sample by breaking the population into homogenous groups e.g. to select 6 students to go for a tour:
- Break the class into boys and girls
- Select 3 student from each group by random or systematic sampling
- Combine units from each group to form the required sample.
Cluster Sampling
-Selection of sample by dividing the sample into clusters with similar characteristics then a sample is taken from each cluster and representative choices from each cluster are combined to form a sample e.g. to sample the housing cost an estate is chosen to represent each group and representative choices are chosen from each estate and combined to form a sample.
Advantages
a) It’s less expensive
b) It saves time
c) It avoids bias
Disadvantages
- a) A poor selected sample can lead to misleading information
- b) Systematic sampling to an evenly distributed population
Experimentation
Experimentation – Conducting a test or investigation to provide evidence for or against a theory e.g. to determine the chemical composition of rocks and soils.
Advantages
a) First hand data is obtained
b) Gives accurate results if properly conducted.
c) It can lead to further discoveries
Disadvantages
a) May be expensive as it involves use of expensive equipment.
b) May be time consuming
c) Use of defective instruments may lead to inaccurate results
d) Improper handling of equipment and chemicals may lead to accidents
