SAMPLING AND EXPERIMENTATION
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.
- a) It’s less expensive
- b) It saves time
- c) It avoids bias
- a) A poor selected sample can lead to misleading information
- b) Systematic sampling to an evenly distributed population
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.
- a) First hand data is obtained
- b) Gives accurate results if properly conducted.
- c) It can lead to further discoveries
- 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