Collection of Data


A distinct piece of information in the form of fact or figures collected or represented for any specific purpose is called Data. 

Collection of Data

Data are generally of two types

  • Primary Data
  • Secondary Data

Primary Data

  • Data collected from any first hand experience for an explicit use or purpose is known as Primary Data

Secondary data

  • Data collected by any third party for a different purpose other than the user is known as Secondary Data.


  • The number of times a particular instance occurs is called frequency in statistics.

Ungrouped data

  • Ungrouped data is data in its original or raw form. The observations are not classified in groups.

Grouped data

  • In grouped data, observations are organized in groups.

Class Interval

  • The size of the class into which a particular data is divided.
  • E.g divisions on a histogram or bar graph.
  • Class width = upper class limit – lower class limit

Regular and Irregular class interval

  • Regular class interval: When the class intervals are equal or of the same sizes.
    E.g 0-10, 10-20, 20-30….. 90-100
  • Irregular class interval: When the class intervals are of varying sizes.
    E.g 0-35, 35-45, 45-55, 55- 80, 80-90, 90-95, 95-100

Frequency table

  • A frequency table or distribution shows the occurrence of a particular variable in a tabular form.


  • Raw data needs to be sorted in order to carry out operations.

Ungrouped frequency table

  • When the frequency of each class interval is not arranged or organised in any manner.

Grouped frequency table

  • The frequencies of the corresponding class intervals are organised or arranged in a particular manner, either ascending or descending.
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