Week 8: Population and Sampling.


In the first case, when saying about the population, we would have to ask the estimation of overall population in large space area. For example, the number of teacher in Selangor. is about 31.7 million people in 2016.  It is obvious that making an interview or distribute questionnaire to more than 30 million people and will required a very huge effort in many field. To make it, there will be long period of time, huge spent of money as it is necessary to employ many people to do interview, and distribute questionnaire. There're a lot of factors need to consider when applying the population and sampling method. Therefore, somehow we ”destroy” this element of the population. If we would have to try each and every battery of the population, we would keep none of them. Thus, what we should do in this situation is also to choose an appropriate sample and then we could take the appropriate general conclusions.

Due to the reasons we have just mentioned, it is convenient in many instances to use samples. But if we want to get really good conclusions from them, we need to assure that we make a right choice of our samples. There are some topics which should be clearly defined once we want to sample: 1. The selection method for the elements of the population (sampling method to be used). 2. Sample size. 3. Reliability degree of the conclusions that we can obtain, this is, an estimation of the error that we are going to have (in terms of probability). As we have just said, a non appropriate selection of the elements of the sample can cause further errors once we want to estimate the corresponding parameters in the population. But we can find some more different types of errors: the interviewer can be partial, this is, he can promote some answers more than others. It can also happen that the person we are going to interview does not want to answer certain questions (or cannot answer).

In this topic, there are 3 subtopic have been focus:-
3.3.1 The Research Population
3.3.2 The research sample
3.3.3 The sampling technique

Population refers to the collection of all elements possessing common characteristics, that comprises universe. It include each and every unit of the group and focus on identifying the characteristics.

The sample is a subgroup of the members of population choose for participation i the study. It include only a handful of units of population. It is focus on making inferences about the population.  

Sampling as the process in which the fraction of the population, so selected to represent the characteristics of the larger group. This method is used for statistical testing, where it is not possible to consider all members or observations, as the population size is very large.

As statistical inferences are based on the sampling observations, the selection of the appropriate representative sample is of utmost importance. So, the sample selected should indicate the entire universe and not exhibit a particular section. On the basis of the data collected from the representative samples, the conclusion is drawn from the whole population.

There are two type of sampling technique:-
1. Probability sampling technique.
2. Non probability sampling technique. 

For probability sampling technique there are 4 types:-
1. Simple random sampling
2. Cluster sampling
3. Systematic sampling
4. Stratified Random Sampling

For non probability sampling technique there are also 4 types:-
1. Convenience sampling
2. Judgmental or purposive sampling
3. Snowball sampling
4. Quota sampling

In my study, i will used the cluster sampling of probability sampling. In this sampling,  we need to choose participants based on clusters. Appropriate when the population of interest is infinite, when a list of the members of the population does not exist, or when the geographic distribution of the individuals is widely scattered.


References: 

Sampling technique: https://keydifferences.com/difference-between-census-and-sampling.html


Taherdoost, H. (2016). Sampling methods in research methodology; how to choose a sampling technique for research. How to Choose a Sampling Technique for Research (April 10, 2016).

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