Classification of data | Explained in detail.

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Compilation of data   or Classification of data Classification of data,definition, methods of classification,class limit,class interval, exclusive and inclusive classes, class frequency,cumulative frequency

 
 
 MEANING  OF  CLASSIFICATION  OR  COMPILATION OF DATA.
     The process of arranging data in groups or classes according to resemblances and similarities is technically called classification. Thus, by classification we try to strike a note of homogeneity in the heterogeneous elements of the collected infomation. Classification gives expression to the similarities which may be found in the diversity of individual units. In classification of data, units having a common characteristic are placed in one class and, in this fashion, the whole data are divided into a number of classes. Even after classification, the statistical data are not fit for comparison and interpretation and need proper tabulation. After tabulation of data, statistical analysis and interpretation are possible. Classification is a preliminary to tabulation and it prepares the ground for proper presentation of statistical facts.
 
     The collected data is often uninteresting. The unorganised and shapeless data can neither be easily compared nor interpreted.Therefore after collection of the data the first step is to present the raw data in some orderly and logical form so that their essential features may become explicit. The  technique of arranging the data in different hemogeneous groups is called classification of the data. Thus a lot of heterogeneous data is subdivided into different groups on the basis of some ‘ common features and after being classified, the data can be tabulated for purposes of interpretation. In other words,classification is the first step to tabulation.
 
According to H. Secrist, “Classification is the process of arranging data into sequences and groups according to their common characteristics or separating them into different but related parts. ”
 
 
Main Objects of Classification.
 
1. Presenting Statistics in a simple Form. The major function of classification is to remove the complexity of Statistics and present them in a simple form. As we know, collected Statistics are very complex and common man cannot understand them and absorb them. By classification Statistics are made simple and as a result it becomes easy to understand them and absorb them.
 
2. Depicting Homogeneity and Heterogeneity of Data. It reveals clearly the points of homogeneity and heterogeneity in the statistical data pass students on one side and fails students‘on the other side.
3.Easy to understand.Classification eliminates unnecessary details so that the salient  features of the collected data are more readily understandable Classification minimises mental strain.
4. Helpful in Comparison. It helps us in comparision. If the data are unorganised and dissimilar, it cannot be compared . So for proper comparison classification of   the data is needed.
5 Increase in usefulness. Classitication helps a person in forming a mental picture of the phenomenon to which the given data relate. Classified data can be easily understood by an illiterate  person.
6. Scientific  Management. Scientific managment of the data is possible if the data are  very  much classified.
3: Attractive and Effective. Classilication helps in making the data very attach and effective.
4.Basis of tabulation. Classification is the basis of tabulation. So tabulation will be proper if the classification is proper.
 4.Presenting Statistics in a Condensed Form. Classification helps in condensation  of data. After collection of data in an enquiry we obtain large number of figures. It is necessary to give these figures a condensed form. This  thing is done by classification.
 6. Helpluf in Presentation of  Statistics. Statistics are presented with tables, graphs or diagrams .This presentation of data requires classification
 7. Helpful in Analysis of Statistics. Analysis of data is the main part of an enquiry.'Data cannot be analysed without classification. For applying any technique of statistical analysis, classification of data is must.
8. For Finding Unnecessary Statistics. While collecting data for an enquiry many unnecessary figures are collected. For judging these unnecessary Statistics  classification renders much help. Therefore  classification is very useful in Statistics.
 
TYPES OF CLASSIFICATION or  METHODS OF CLASSIFICATION.
        Statistical data are classified according to the characteristics possessed by them. These common characteristics reveal the homogeneity of a group of units in the whole lot of heterogeneous data. These characteristics can either be descriptive or numerical. Descriptive characteristics cannot be quantitatively measured, only their presence or absence in an individual unit can be found, e.g. sex, nationality, literacy etc. cannot be quantitatively expressed. What we can do is to determine whether an individual is literate or illiterate. employed or unemployed. Numerical characteristics, on the other hand, are capable of quantitative measurement. e.g. height, weight etc. When the data are classified on the basis of descriptive characteristics which cannot be expressed quantitatively. the classification is said to be according to the attributes and when the data are classified on the basis of quantitative measurement the classification is said to be according to the class intervals on the basis of attributes and class intervals the classification is of different types.
  Thus, broadly speaking, data can be classified on the following four bases :
 
1.Spatial or Geographical, i.e., in relation to place
2. Chronological, i.e., on the basis of time
3. Qualitative, i.e., according to some attributes  
4. Quantitative, i.e., in terms of magnitude.
 
1.    Geographical Classification : ln geographical classification, data are classified on the basis of place. If, for example. we write down the population of the Indian Union on the basis of various States or if we write down the number of students in different universities of the country, or production of wheat in different geographical areas of the country, the series that we would get would need classification on the basis of geographical distribution. Series which are arranged on the basis of place are called spatial series.
          It is a classification based on geographical regions. If the existing political boundaries are taken as the basis, the classification may be  done by states and districts. e. g.
The following is an example of a geographical distribution :

Country	National income in U. S. dollars
Canada	7930
USA	7880
West Germany	7510
France	6730
U. K.	4180
U. S. S. R.	2800
India	140

 
Geographical classifications are generally listed in alphabetical order or listed by the frequency size to emphasise the importance of various geographical regions .
 
2.    Chronological classification : When the data are classified on the basis of time, then it is known as  chronological classification. Such series are also known as time series because one of the variables in them is ‘time. 1f the population of India during the last eight censuses is classified, it will result in a time series or chronological classification.In such a classification , data are classified either in ascending or in descending order with reference to time such as years, quarters,months ,weeks etc.  It is also called temporial  classification.
 
The following table would give an idea of chronological classification :

year	Production( soap) company X
1995	12800
1996	13988
1997	14288
1998	15779
1999	16827
2000	16989
2001	17828

 
Qualitative   classification;
       Classification according to Attributes. When the data are classified on the basis of presence or absence of some attribute, which is incapable of quantitative measurement, it is a descriptive classification or a classification by attributes. Descriptive classification is of two types:
(a)     Simple classification. In this method the entire statistical data are divided on the basis of presence or absence of a particulat attribute. All those units which possess a particular attribute are put in one group and the other with the absence of such an attribute are placed in another group, e.g. literacy and illiteracy, male and female etc.  e,g                                               Population                                 
                                   Male                                     not male (female)
(b) Manifold Classification. In this case we study more than one attribute simultaneously, the statistical data will be divided into more than two classes, e, g on the basis of language, we classify Hindi language, Gujarati language, Bengali language etc.  
                                                            FEMALE          Married  unmarried                                          Married  unmarried   
LITERATE     ILLITERATE  LITERATE     ILLITERATE                    LITERATE     ILLITERATE  LITERATE      ILLITERA
 
3.    Quantitative, i.e., in terms of magnitude. 
 CIassification according to the class-intervals. The difference between the upper limit and the lower limit is known as class interval, or quantitative classification . It is a classification which is based on  such characteristics which are capable of quantative  measurement. Such characteristics can be height, weight,income,expenditure,number of marks obtained by students of a class etc': e,g
Continuous series

Marks ( class interval)	No. of  students (frequency)
0-20	5
20-40	15
40-60	25
60-80	10
80-100	5
TOTAL	60

 
Discrete series

Marks	No. of  students
2	5
3	15
4	25
5	10
6	5
TOTAL	60

 
     In this type of classification following terms are used: '
(a) Class limit. The class limits are the lowest and the highest values that can  be included in the class. The two boundaries of a class are known as the lower limit and the upper limit of the class, e. g. in the class 10-20, 10 is the lower limit and 20 is the upper limit.
 
(b) Magnitude of class-interval. The difference between upper limit and lower limit called the magnitude of class interval.
 
(c)  MId-Value. It is the value lying haIf-way between the lower and upper cIass limits of a cIass-interval. Mid-point of a class is ascertained as follows:
                            Upper limit+ lower limit Mid value=                                                          2  
 
 
 
 
 
 
 
 
 
 
Exclusive method;

Marks ( class interval)	No. of  students (frequency)
0-20	5
20-40	15
40-60	25
60-80	10
80-100	5
TOTAL	60

Inclusive method;

Marks ( class interval)	No. of  students (frequency)
10-19	5
20-39	15
40-59	25
60-79	10
80-99	5
TOTAL	60

 

Marks ( class interval)	No. of  students (frequency)
9.5-19.5	5
19.5-39.5	15
39.5-59.5	25
59.5-79.5	10
79.5-99.5	5
TOTAL	60

Cumulative frequency;

Marks	No. of  students	Cumulative frequency
2	5	5
3	15	20
4	25	45
5	10	55
6	5	60
TOTAL	60

 
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Manifold Classification       Population of india

                   ' MALE,