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Collection and Presentation of Data

A systematic record of facts or different values of a quantity is called data. Data is of two types - Primary data and Secondary data. The data collected by a researcher with a specific purpose in mind is called primary data. The data gathered from a source where it already exists is called secondary data.
The difference between the highest and lowest values in the given data is called the range of the given data. The number of times a value occurs in the given data is called the frequency of that value.

A table that shows the frequency of different values in the given data is called a frequency distribution table. A frequency distribution table that shows the frequency of each individual value in the given data is called an ungrouped frequency distribution table. A table that shows the frequency of groups of values in the given data is called a grouped frequency distribution table.
The groupings used to group the values in given data are called classes or class-intervals. The number of values that each class contains is called the class size or class width. The lower value in a class is called the lower class limit. The higher value in a class is called the upper class limit.