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Sunday, December 16, 2012

Guwahati University - M.Com Solved Assignments - Paper V (1st Year)


Q.N. 2. What is Sampling? Critically examine the well –known methods of probability and non-probability sampling?
Ans: It is important for the investigator to decide whether to use sample or census method for collecting data. The selection primarily depends upon the nature and extent of the enquiry and the degree of accuracy desired. At the same time, the scope of the enquiry, its cost, the time of enquiry, the selection and training of the enumerators etc. are also to be taken into account. Basically, accuracy and precision depends upon the human element. If the human element is perfectly impartial and unbiased then best results can be expected from either method. In the absence of it, the results may be distorted.
Both the methods of enquiry have their individual merits and demerits. For example the sampling method is suitable in case of large population, where as census method is preferred in case of small population. In this connection S. S. Zarkovie rightly observes, “complete enumeration presupposes the existence of certain minimum facilities; such as-funds, professional personnel, sufficient time etc. These facilities do not always exist and therefore, it sometimes becomes impossible to take a census. Similarly recourse to sampling makes it possible to obtain information in a number of cases where a complete enumeration cannot be undertaken”. Both the systems of enumeration are useful and advantageous at different occasions. So both or any of these methods may be followed according to the need or environment.

Types of Sampling:
In the sampling method a representative group of items from the population are selected. These groups of items are called samples. These samples represent the whole universe. Therefore the selection of samples is crucial in this method. It is rightly said, “Samples are like medicines. They can be harmful when taken carelessly or without knowledge of their effects. Every good sample should have a proper label with instructions about its use”. So while selecting samples, a number of factors should be considered. Some of the important factors are:
a)      the nature of the population
b)      the distribution of items in the population
c)       the characteristics to be studied
d)      availability of data
e)      availability of both financial and human resources etc.
Considering these factors a choice is made regarding the type of samples to be used. Generally there are two methods of selecting samples
1. Probability sampling method or Random sampling method
2. Non- probability (purposive) sampling method

Probability sampling method:
Probability sampling is also known as choice sampling. Here each individual item of the population has same chance of being included in the sample. So here the selection of the units in the sample entirely depends on the chance factor. One does not know beforehand which units will actually constitute the sample. Probability samplings are of different types. Some of the important types of probability sampling are.

a) Sample random sampling: - Simple random sampling requires that the number of units in the population be known and each unit is assigned a number. A specific quantity of random numbers between one and total number of population units is selected. Sample size is determined by lot size and potential impact of a consumer or vendor error. Units corresponding to the random numbers are then analyzed as an estimate of the population.
b) Systematic Sampling:-Systematic sampling is used when a complete list of sample units is not available, but when samples are distributed evenly over time or space, such as on a production line. The first sample is selected at random and then every nth unit after that.
c) Stratified Sampling:-Stratified sampling involves dividing the population into overlapping subgroups so that each subgroup is as homogenous as possible. Group means, therefore, differ from each other as much as possible. Random samples are then taken from each subgroup. The procedure provides a representative sample because no part of the population is excluded and it is less expensive than simple random sampling.
d) Cluster Sampling:-Cluster sampling entails dividing the population into clusters or subgroups so that cluster’s characteristics are as identical as possible, that is, the means are very similar to each other. Any heterogeneity occurs within each cluster. Clusters should be small and having a similar number of units in each cluster. The clusters are sampled randomly and may be either totally inspected or sub sampled for analysis. This sampling method is more efficient and less expensive than simple random sampling, if populations can be divided into homogenous groups.
e) Composite Sampling:-Composite sampling is used to obtain samples from bagged products such as flour, seeds, and larger items in bulk. Two or more samples are combined to obtain one sample for analysis that reduces differences between samples. For example, FDA composite 12 and at least six subsamples, respectively, for the sample to be analyzed for compliance with nutrition labeling regulations.

Types of Non-Probability or Purposive Sampling
Following are the main types of purposive sampling.
a)      Quota Sampling: It is a type of purposive sampling in which the whole universe is divided first into certain parts and the total sample is allocated among these parts! Each part of' the population is assigned to an investigator for whom the quota of the units to be examined by him is fixed in advance according to certain specified characteristics such as sex, age, occupation, income group, political or religious affiliation. The invigilator is asked to select the required number of units of the sample of his own accord and examine them to get the desired information as quickly as possible. He is also authorized to substitute the new units in the quota if he finds that any unit of the sample so selected is not responding up to the mark. This method is very often used in opinion poll surveys, market surveys and political surveys.

Example: Suppose we make a public opinion survey of "New Budget of Govt, of' India-2003" In quota sampling, interviewers are asked to interview a total 1000 persons of the area allotted. It has also been asked that out of each 100 persons 80 are housewives, 30 are farmers, 30 are industrialists, 20 are transporters and 20 are fixed salary persons. In this way, each category will have its quota. In our example, housewives' 400, of farmers 200, industrialists 200, transporters 100, and the fixed salary persons 100.

Merits
(i) Purposive Sampling: - It enjoys all the advantages of purposive or judgment sampling.
(ii) Reliable Results:-It gives more reliable and dependable results, if the investigators are skilled the experienced and their works are properly supervised.
(iii) Economical:-There is considerable saving in time and money as the sampled units may be so selected that they are close together.

Demerits
(i) It suffers from all the defects of a purposive sampling.
(ii) Scope of Mischief:-The investigator is free to play mischief in the selection of the items of the sample and collection of the data.
(iii) Not Possible to Estimate Sample error:-It is not possible to estimate the sampling error and the degree of accuracy achieved.

b)      Convenience Sampling: It is a type of purposive sampling in which the sample units are selected purposively by the investigator to suit his convenience in the matter of location and contract with the units.
This method of selecting the sample is also called 'Chunk' since the samples under this method are selected neither on the basis of the rules of probability nor on the basis of the judgment of the investigator but on the basis of convenience on the part of the investigator.
For example, a sample obtained from a list of students in a college for enquiring into their educational problems, is a matter of convenience sampling as in such a case it will be convenient for the investigator to locate and contract the selected students for obtaining the desired information from them.
Example
Suppose we have to study the problems faced by Sugar Industry in Uttar Pradesh. Now, if we choose 20 units which are in our easy command, sampling technique will be termed as convenience sampling.
Merits
(i) Easy Command:-The units of the sample are easily located and contacted by the investigators.
(ii) Economical:-It is less expensive and less time consuming.
(iii) Suitable for Pilot Surveys:-It is suitable for making pilot surveys in which questions are pre-tested and preliminary information's are obtained before finalizing the sample design.

Demerits
(i) Does not represent Universe:-The units of the sample selected under this method hardly represent the universe.
(ii) Bias:-It is very much influenced by the bias and personal convenience of the investigator.
(iii) Unsatisfactory Results:-The results obtained under this method are found to be unsatisfactory and misleading.
(iv) Personal convenience of Investigator:-It is based neither on the rules of probability nor on the principle of judgment but on the personal convenience of the investigator.