Lect #3 Frequency Distribution

Frequency Distribution An important method for summarizing and organizing quantitative data is the formation of a frequency distribution.

Frequency Distribution A frequency distribution is a tabular arrangement of data in which various items are arranged into classes and the number of items falling in each class (called class frequency) is stated. Data presented in this form of frequency dist. Is also called grouped data. Data which have not been arranged in this form is called raw data or ungrouped data.

Class Limits and Class Boundaries Each class is described by two numbers. These no. are called class limits; the smaller no. is called the lower class limit and the larger no. is upper class limit.

Class Limits and Class boundaries Class limits are not always exactly what they look like. The true limits of a class are called class boundaries. The smaller value is called lower class boundaries and larger value is called upper class boundaries. Class boundaries are not always halfway the stated class limits. for discrete variables, C.B.are the same as C.l.

Open –end classes Sometimes , frequency tables are formed in which a class has either no lower class limit or no upper class limit.Such a class is open end class.

The Class Marks or Midpoints That value which divides the data into two equal parts.it is obtained by adding the lower and upper class limits or class boundaries of a class and dividing the resultant by 2

Size of class interval The size of class interval also called class width or class length is the difference b/w the upper class boundary and the lower class boundary

Formation Of Frequency Distribution • Determine the greatest and the smallest number in the raw data and find range ,i.e., the difference b/w thr greatest and the smallest value • Decide the no. o classes • Determine the approximate class interval size by dividing the range by the desirable no. of classes • Decide what should be the lower class limit • Find the upper class limit by adding the class interval size • Describe the values in the raw data into classe and determine the no. of cases falling in each class i.e., class frequency