Discuss the important types of classifying data with illustration.
Discuss the important types of classifying data with illustration.
Or
What are the objects of classification of data? Explain classification according to attributes and classification according to class intervals?
Ans.
Methods of Classification
Statistical facts are of two types: (i) Descriptive, and (ii) Numerical Descriptive factors can not be measured directly. The study about say attributes is measured on the basis of its Presence or Absence. For example, literacy, unemployment, marital status etc. are descriptive facts which cannot be measured directly. Only number of illiterates and illiterates or number of married and unmarried persons in an area can be determined. Such facts are called ‘attributes’ in statistics. On the other hand numerical facts are such which can be measurable directly, for example income, age, height, weight etc. These facts are also called variables. On the basis of these two facts, there are two methods of classification as under :
(a) Qualitative Classification or Classification according to attributes,
(b) Quantitative Classification or classification according to class intervals.
(a) Qualitative classification: When facts are classified on the basis of descriptive attributes like ‘literacy’ ‘religon’ profession etc. it is called qualitative classification. It may be of two types :
(i) Classification according to Dichotomy: When facts are classified on the basis of presence or absence of one attribute only, the classification is called dichotomous or simple. The presence of attributes is expressed in capital letters, such as A, B, C etc. and the absence in terms of small letters such as a, b, c etc. or Greek letters a (Alpha), B (Beta), y (Gamma) etc. On the basis of literacy, literates will be represent by (A) and, to illiterates by (a). It is called simple or dichotomy classification.
(ii) Manifold Classification: In manifold classification, the facts are classified on the basis of more than one attribute for which more than two groups are formed. First two groups are formed on the basis of one attribute and there after each group is subdivided into two sub groups on the basis of another attribute. Thus, more than two groups and sub-groups are formed.
(b) Quantitative Classification or Classification According to class-intervals : Numerical facts are classified usually on the basis of class-intervals. The smallest and the largest numbers keeping in considerations, the data are classified into different groups as per the convenience.
(i) Class-Limit: The two values which determine the limits of a group are called class limits. The first value or lower value is called Lower limit, whereas the second value or higher value is called upper limit. Lower limit is expressed by l1 symbol and the upper limit by l2, symbol.
(ii) Magnitude of Class-interval: The difference between the upper and lower limits of a class group is called magnitude of the class interval. It is expressed by the symbol ‘i’. Thus i = l2 – l1.
(iii) Mid-value or Mid-point: The central place of a class group is called Mid value or mid point or central size. It is obtained by dividing the sum of both the limits by 2, that i.e.
Mid-point = l1/2 +l2/2
(iv) Class-frequency: In numerical classification, it is necessary to know the number of observation or number of items included in a particular class group. The number of such units is called number of items of the included in a particular class group. The number of such units is called number of items of the frequency of that class.
