Mathematics: You Must Know the Important Facts about Statistics for Competitive Exam Preparation

Important Facts about Statistics

Collection of Data

Collection of data is the first step in statistics towards achieving the goal on conclusion. There are different sources of collection of data.

There are three main type of data on the basis of collection are as follows

• ( i ) Primary Data: The data collected actually in the process of investigation by the investigator is known as primary data.
• ( ii ) Secondary Data: Data which is already collected by other persons is called as secondary data

Ex:- As investigator collects data related to industries through the government publication.

• ( iii ) Raw Data: It is ungrouped data. If the data is large, the need is to condense the data according to the need of the user. It could be presented into classes of groups. The rules in setting up classes are

• a) Classes should be without gaps in between and also should be non-overlapping.

• b) Classes, normally, should be of the same size.

• c) Normally, open-ended classes should not be formulated.

• d) Each class must have a lower limit and upper limit. The difference between both the limits is called the class interval.

Methods of Classification of Data:

( i ) Exclusive Method:

When the class intervals are so fixed that the upper limit of one class is the lower limit of the next class, it is known as the exclusive methods of classification. In this method, the upper limit of a class is not included in the class. Thus, in the class 0-10 of marks obtained by students, a student who has obtained 10 marks is not included in the class. He is counted in the next class of 10-20.

( ii ) Inclusive Method:

In this method, the classes are so formed that the upper limit of a class is included in the class. 

Important Definitions:

• 1. Frequency: The number of times a particular observation occurs is called frequency of that observation.

• 2. Class Frequency: The frequency of a class in a continuous frequency distribution is called as class frequency.

• 3. Class Mark: It is the mind value of the class interval.

                         

                        Lower limit of class + Upper limit of class

Class Mark =   ---------------------------------------------

                                         2

• 4. Range: It is the difference between the highest and the lowest values of the observation.

                  Range = Maximum observation -  Minimum observation

Ex:- Range of the observations 4, 7, 8, 10, 12

                    = 12 - 4 = 8

• 5. Cumulative Frequency: The cumulative frequency of a class interval is the sum of frequencies of all classes up to that class including the frequency of that particular class.