Classification of Data: The process of grouping data according to their characteristics is known as classification of data.

Objectives of Classification:

1. To simplify complex data: The main objective of classification is to condense the large data to make them easily understood.
2. To facilitate understanding
3. To facilitate comparison
4. To make analysis and interpretation easy.
5. To arrange and put the data according to their common characteristics.

 Statistical Series: Systematic arrangement of statistical data

1. Can be on the basis of individual units :

 The data can be individually presented in two forms:

i] Raw data: Data collected in original form.

ii] Individual Series: The arrangement of raw data individually. It can be expressed in two ways.

• Alphabetical arrangement : Alphabetical order
• Array: Ascending or descending order.

1. Can be on the basis of Frequency Distribution:

 Frequency distribution refers to a table in which observed values of a variable are classified according to their numerical magnitude.

1. Discrete Series: A variable is called discrete if the variable can take only some particular values.

2. Continuous Series: A variable is called continuous if it can take any value in a given range. In constructing continuous series we come across terms like:

• Class : Each given internal is called a class e.g., 0-5, 5-10.
• Class limit: There are two limits upper limit and lower limit.
• Class interval: Difference between upper limit and lower limit.
• Range: Difference between upper limit and lower limit.
• Mid-point or Mid Value: Upper limit – Lower limit 2
• Frequency: Number of items [observations] falling within a particular class.

1. Exclusive Series: Excluding the upper limit of these classes, all the items of the class are included in the class itself. E.g., :

2. Inclusive Series: Upper class limits of classes are included in the respective classes. E.g.,

3. Open End Classes : The lower limit of the first class and upper limit of the last class are not given. E.g.,

4. Cumulative Frequency Series: It is obtained by successively adding the frequencies of the values of the classes according to a certain law.

1. Less than’ Cumulative Frequency Distribution : The frequencies of each class-internal are added successively.
2. More than’ Cumulative Frequency Distribution: The more than cumulative frequency is obtained by finding the cumulative totals of frequencies starting from the highest value of the variable to the lowest value.

Data – Information which can be expressed in numbers.

 Primary vs. Secondary Data

Data can be collected in two different ways. One way is to collect data directly from

the respondent. The person who answers the questions of the investigator is called

respondent. Statistical information thus collected is called primary data and the

source of such information is called primary source. This data are original because

it is collected for the first time by the investigator himself. For example, if the

investigator collects the information about the salaries of National Institute of technology employees of then it is primary data for him.

Difference between Primary and Secondary Data

1. Primary data is original data collected by the investigator while secondary data is already existing and not original.
2. Primary data is always collected for a specific purpose while secondary data has already been collected for some other purpose.
3. Primary is costlier or is more expensive whereas secondary data is less expensive.

Methods / Sources of Collection of Primary Data :

There are several methods for collecting primary data. Some of which are:

1.Direct personal interview : In this method investigator (also called interviewer)

has to be face-to-face with the person from whom he wants information. The

person from whom this information is collected to called respondent.

2.Indirect oral investigation : Under this method data are collected through

indirect sources. Under this method questions relating to the inquiry are put

to different persons and their answers are recorded. This method is most

suitable when the person from whom the information is sought is either

unavailable or unwilling.

3.Information from correspondents – Data is collected from agents appointed in the area of investigation.

4.Questionnaire method : In this method a list of questions called questionnaire

is prepared and sent to respondents either through post or given personally to

them. This method is suitable where the field of inquiry is wide.

There are some advantages of using primary data. The investigator can collect

the data according to his requirement. It is reliable and sufficient for the

purpose of investigation. However, it suffers from disadvantages also in that

it involves a lot of cost in terms of money, time and energy. This make

unsuitable when field of enquiry is very very large. Many a times with some

modifications, same purpose may be served by using data collected by other

persons or agencies.there two types Questionnaire

1. Mailed questionnaire – Data is collected through questionnaire [list of questions] mailed to the informant.

1. Questionnaire filled by enumerators – Data is collected by trained enumerators who fill questionnaires.

Qualities of a good questionnaire :

A covering letter with objectives and scope of survey.

Minimum number of questions.

Avoid personal questions.

Questions should be clear and simple.

Questions should be logically arranged.

Sources of secondary data

As already discussed secondary data are not collected by the investigator himself

but they are obtained by him from other source. Broadly, there area two sources:

(a) Published data and (b) Unpublished data.

Published Sources

There are certain agencies which collect the data and publish them in the form of

either regular journals or reports. These agencies/sources are known as published

sources of data.

In India some of the published sources are:

1. Central Statistical Organisation (CSO) : It publishes data on national

income, savings, capital formation etc., in a publication called National

Accounts Statistics.

2. National Sample Survey Organisation (NSSO) : This organization which

is under the Ministry of Finance provides data on all aspects of national

economy, such as agriculture, industry, employment and poverty etc.

3. Reserve Bank of India (RBI) : It publishes financial statistics. Its publications

are Report on Currency and Finance, Reserve Bank of India Bulletin and

Statistical Tables Relating to Banks in India etc.

4. Labour Bureau : Its publications are Indian Labour Statistics, Indian Labour

Year Book and Indian Labour Journal.

5. Population Census : It is undertaken by the office of the Registrar General,

Census of India, Ministry of Home Affairs. It provides us statistics on

population, per capita income, literacy rate etc.

6. Papers and Magazines : Journals like ‘Capital’, ‘Commerce’, Economic and

Political Weekly’, and newspapers likes ‘The Economic Times’ etc. also

publish important statistical data.

Unpublished Sources

Secondary data are also available from unpublished sources, because all statistical

data is not always published. For example, information recorded in various

government and private offices, studies made by research scholars etc. can be

important sources of secondary data.

Difference between census method and sampling method.

Mailed Questionnaire Method:

Meaning of Statistics in plural sense : In plural sense statistics means statistical data ‘‘By statistics we mean aggregate of facts affected to a market extent by multiplicity of causes numerically expressed enumerate or estimated according to a reasonable standard of accuracy, collected in a systematic manner for a predetermined purpose and plural in relations to each other.

Meaning of Statistics in Singular Sense :-In the singular sense, statistics means science of statistics or statistical methods. If refers to techniques or methods relating to collection, classification, presentation, analysis and interpretation of quantitative data. These are the stages through which every statistical enquiry has to pass through.

Consumer – A person who buys goods and services for the satisfaction of human wants.

Producer – A person who produces goods.

Service holder – A person who is working or in a job and gets paid for it.

Service Provider – A person who gives services to others for a payment.

Economic activity – Activities undertaken for monetary gain or to earn income.

Economics is divided into three parts:

1. Consumption
2. Production

• Distribution

1. Consumption: In consumption, we study wants, their origin, nature and characteristics and the laws governing them.
2. Production: It refers to all activities which are undertaken to produce goods and services for generation of income and satisfaction of wants.

• Distribution: Economic activity which studies how income generated from the production process is distributed among the factors of production.

 Data: Economic facts in terms of numbers.

Characteristics of Statistical Data

(i) Statistical data are aggregates of facts:A single observation is not statistics, it is a group of observations. For example, Ram scored 60 marks out of 100 is not statistics, but a series relating to the marks of a group of students will be termed as statistics. For example, when we say that Mohan, Ram, Mary and Karim scored 35, 60, 75 and 58 marks respectively, the group of figures become statistics.

(ii) Statistics are affected by multiplicity of causes : Generally the facts and figures are affected by a number of factors working together. For example, the production of rice depends on rainfall, method of cultivation, seeds, manure, soil fertility etc. but it is very difficult to study separately the effect of each of these factors on the production of rice.

(iii) Statistical data are numerically expressed : All statistics are numerically expressed. Qualitative statements such as ‘the population of India is increasing rapidly’ or ‘India’s per capita income is low’ are not statistics unless they are assigned numerical values.

(iv) Collected in a systematic manner : Statistics should be collected systematically in a planned way. Before collecting data, a suitable plan for their collection should be prepared. Data collected in an unsystematic manner would lead to misleading conclusions.

(v) Statistical data must be obtained with reasonable degree of accuracy : Statistics are numerical statements which can be obtained with accuracy if the number of observations is small. Sometimes, when actual measurement of figures is not possible in a particular field of inquiry, then method of estimation or approximation is applied. For example, if we say that there are 30 students in XI class of XYZ public school, the figure is 100 percent accurate if we apply counting method. But, on the other hand, if we say that 20,000 people are watching the cricket match, this figure can be obtained only by estimation method i.e. as an approximation. But even this estimation must have a reasonable degree of accuracy to make sense.

(iv) Statistics are collected for a predetermined purpose : The purpose of collecting data should be decided in advance. The purpose should be clearly defined. Otherwise, collected data will be of no use. Suppose, we want to compare the performance of students at secondary level of National Institute of Open Schooling in one subject or more. We must specify the subjects and the year for which comparison is being carried out before collecting data.

14. Importance of Statistics:

(a) Statistics and the study of consumption: Every individual needs a certain number of things. He spends first on necessities, then on comforts and luxuries, which depend on his income. We discover how different groups spend their income on different items of consumption with the help of statistics.

(b) Statistics and the study of production: The progress of production every year can easily be measured by statistics. The comparative study of productivity of various elements of production (e.g. land, labour, capital and entrepreneurship) is also done with the help of statistics. The statistics of production are very helpful for adjustment of demand and supply.

(c) Statistics and the study of exchange: Production is based on national and international demand. A producer needs statistics for deciding the cost of production and selling price so that he can study competition and demand of commodity in a market. The law of price determination and cost price which are bared on the various market conditions and demand and supply can be studied with the help of statistics.

(d) Statistics and the study of distribution: Statistics are helpful in calculation of national income in the field of distribution statistical methods are used in solving the problem of the distribution of national income. Various problems arise due to unequal distribution of wealth and national income and are solved with the help of statistical data.

Limitation of statistics

(i) It does not study the qualitative aspect of a problem: Statistics studies only the facts which can be measured quantitatively but qualitative phenomena like honesty, intelligence, poverty etc. cannot be studies in statistics unless these attributes are expressed in terms of numerals.

(ii) It does not study individuals: Statistics studies aggregates of facts but individual values of the observation like income of a family has no specific importance.

(iii) Statistical laws are true only on an average: Since the results are affected by a large number of cause, laws of statistics are not universally applicable.

(iv) Statistics can be misused: The results obtained with the help of statistics can be manipulated according to one’s own interest which can mislead the community.

(v) Statistical results lack mathematical accuracy: The results drawn from statistical analysis are normally in approximations. So statistical studies are a failure in the fields where cent per cent accuracy is desired.