Class XI:Statistics [Ch-3 Census and Sample Methods of Collection of Data]

Concepts of ‘Census’ and ‘Sample’

Census Method

Census method is that method in which data is collected covering every item of the universe or population relating to the problem under investigation.

SUITABILITY OF CENSUS METHOD

Senses method is suitable particularly for such statistical investigations which have (1) small size of population, (2) widely diverse items in the population, (3) requirement of intensive examination of different items, and (4) high degree of accuracy and reliability. 

Merits

Principal merits of census are as under:

1. Reliable and Accurate:

Results based on census methods are accurate and highly reliable. This is because each and every item of the population is studied.

2. Less biassed:

Results based on census methods are less biassed. It is because of the absence of investigator’s directly regarding the selection of sample items.

3. Extensive Information:

Information collected through the census method is quite exhaustive and therefore, more meaningful because all the items of a universe are examined. For example, population census in India gives exhaustive information relating to the number of people in different parts of the country, their age and sex composition, education, status, occupation, and the like.

4. Study of  Diverse Characteristics:

By using census methods, one can study diverse characteristics of the universe.

5. Study of Complex Investigation:

When items in a universe are of complex nature and it is necessary to study each item, only the census method can produce the desired result. Data on a country's population is collected by this method.

6. Indirect Investigation:

Census methods can be successfully used in indirect investigations related to unemployment, poverty, corruption, etc.

Demerits

However, there are certain demerits of census method as under

1. Costly:

The Census method is very costly and is, therefore, generally not used for ordinary investigations. Only the Government or some big institutions can afford to use this method and that too for specific purposes only.

2. Large Manpower:

Census method requires a lot of manpower. Training a large number of enumerators becomes essential, which is a very difficult process.

3. Not Suitable for Large Investigations:

If the universe comprises a large number of items, then it may not be possible to cover each and every item. The Census method becomes particularly inoperative in such situations.

Sample Method

Sample method is that method in which data is collected about the sample on a group of items taken from the population for examination and conclusions are drawn on their basis.

SUITABILITY OF THE SAMPLE METHOD

Sample method is particularly suitable when: (1) the size of the population is very large, (2) a very high degree of accuracy is not needed, (3) intensive examination of diverse items is not required, and (4) when different units of the universe are broadly similar to each other.

Merits of the Sample Method

Some of the principal merits of the sample method are as under:

1. Economical:

Sample method of investigation is economical because only some units of the population are studied.

2. Time Saving:

In this method, only a limited number of items are investigated. As such the process of investigation is time-saving, not time-consuming.

3. Identification of Error:

Because only a limited number of items are covered, errors can be easily identified. To that extent the sampling method shows better accuracy.

4. Large Investigations:

Sample method is more feasible in situations of large investigations than the census method which generally involves unaffordable cost.

5. Administrative Convenience:

There is an administrative convenience in handling a limited number of items. More capable and efficient investigators can be appointed.

6. More Scientific:

According to R. Fisher, Sample Method is more scientific because the sample data can be conveniently investigated from various angles.

Demerits of the Sample Method

Yet there are some demerits of the sample methods as under:

1. Partial:

It is only a partial investigation of the universe. The investigator’s bias in the selection of the sample is not ruled out. Accordingly, the results may be biassed as well.

2. Wrong Conclusions:

If the selected sample does not represent the characteristics of the universe, the study may end up with wrong conclusions.

3. Difficulty in Selecting Representative Sample:

It is not very easy to select a sample which would represent the characteristics of the entire population.

4. Difficulty in Framing a Sample:

Sometimes the universe may be so diverse that it becomes difficult to frame a sample.

5. Specialised Knowledge:

Sampling involves a set of technical procedures. One must have the technical knowledge of choosing a representative sample from the universe. Persons who are well-versed with all the techniques of sampling are not easily available.

Essentials of a Sample

1. Representative:

A sample must represent all the characteristics of the universe. It is possible only when each unit of the universe stands equal chances of being selected in the sample.

2. Independent:

All units of a sample must be independent of each other.

3. Homogeneity:

If more than one sample are selected from a universe, these samples should be homogeneous (and not contradictory) to each other.

4. Adequacy:

The number of items in the sample should be fairly adequate so that some reliable conditions are drawn covering the characteristics of the universe as a whole.

Methods of Sampling

1. Random Sampling

Random sampling is that method of sampling in which each and every item of the universe has an equal chance of being selected in the sample.

2. Purposive or Deliberate Sampling 

Purposive sampling is that method in which the investigator himself makes the choice of the sample items which in his opinion are the best representative of the universe.

3. Stratified or Mixed Sampling

According to this method of sampling, the population is divided into different strata having different characteristics and some of the items are selected from each strata, so that the entire population gets represented.

4. Systematic Sampling

According to this method, units of the population are numerically, geographically and alphabetically arranged. Every nth item of the numbered items is selected as a sample item.

5. Quota Sampling

In this method, the population is divided into different groups of classes according to different characteristics of the population.

6. Convenience Sampling

In this method, sampling is done by the investigator in such a manner that suits his convenience.