The word data means information or set of given facts in numerical figures It is the science which deals with the collection, presentation, analysis and interpretation of numerical

Primary Data : The data collected by the investigator himself with a definite plan in mind are known as primary data Secondary Data : The data collected by someone, other than the investigator, are known as secondary data

The data obtained in original form are called ungrouped data We may condense data into classes or groups. Such a presentation is known as grouped data An arrangement of raw numerical data in ascending or descending order of magnitude, is called an array Putting the data, in the form of tables, in condensed form, is known as the presentation of data The number of times an observation occurs is called its frequency

A frequency distribution in which each upper limit of class is excluded and lower limit is included A frequency distribution in which each upper limit as well as lower limit is included

Any character which is capable of taking several different values is called a variable Each group into the raw data is condensed, is called class interval The difference between the true upper limit and the true lower limit of a class

Upper limit + lower limit 2 The difference between the maximum value and the minimum value of the variate

The cumulative frequency corresponding to a class is the sum of all frequencies up to and including that class

sum of observations Mean = number of observations