Before you know why you should use sample in your research, here are some terminology you should understand
- Sample, this is the finite part of statistical population whose properties are studied to gain information about the whole. When dealing with people, it can be defined as set of respondents selected from large population for the purpose of survey.
- Population, this is group of individual person, objects or items from which sample are taken for measurement. For example a population of book, presidents,teachers or students.
- Sampling, is the act, process or technique of selecting a suitable sample or representative part of the population for the purpose of determining parameters or characteristics of the whole population.
- A sampling frame, is the specific data from which sample is drawn for example telephone book
The following are 6 reasons sample should be used your research studies.
- The time factor – sample may provide you with the needed information quickly. For example, you are a doctor and disease has broken out in the area of your jurisdiction, the disease is contagious and it is killing within hours, nobody knows what it is. You are required to conduct a quick test to save the situation. If you try the census of those affected, they will be long dead before you arrive with your results. In such a case, the study of just a few of those already infected could be used to provide the required information.
- Accuracy of sampling, a sample may be more accurate than the census. A sloppily conducted census can provide reliable information than a carefully obtained sample
- Reduced cost – it is obviously less costly to obtain data for a selected subset, rather than the entire population. Furthermore, data collected through a carefully selected sample are a highly accurate measure of a larger population
- The large size of many populations – in some cases the size of the population is extremely large. For example, if you conduct research studying all elementary school students in a particular country, it is difficult to reach all the students because of their large number. To do this kind of research you need a sample.
- Destructive nature of some studies. In some studies for example quality control studies, the only way to know the characteristics of the sample unit is through destroying them. Therefore, to know the characteristics of these sample units you only need a sample to study them. Another example is when a doctor wants to do a blood test, he only needs to take a sample because if he drains all blood out of the patient, the patient will definitely die.
- Lastly, in some cases, it is impossible to identify all units in the population. For example, it is impossible to identify all air molecules in Dar es Salaam. So to measure air pollution you take a sample of air molecules. Also, even if all air molecules could be identified, it would be too expensive and too time-consuming to measure them all.