Concept about No of observations, Maximum and minimum value,
Frequency distribution and cumulative Frequency distribution
Determine the range of variation
Class width determination
Location of class limit
1. Course Title: Business Statistics
BBA (Hons)
2nd
Semester
Course Instructor: Atiq ur Rehman Shah
Lecturer, Federal Urdu University of Arts,
Science & Technology, Islamabad
+92-345-5271959
aatresh@gmail.com
2. Learning Objective
• Concept about No of observations,
Maximum and minimum value,
• Frequency distribution and cumulative
Frequency distribution
• Determine the range of variation
• Class width determination
• Location of class limit
3. Raw Data: IT Department Graduate Level (MCS)
Maximum Minimum
Number of observations = 27
4. Frequency Distribution
• A representation, either in a graphical or
tabular format, which displays the number of
observations within a given interval.
• The intervals must be mutually exclusive.
5. Steps:
1. Deciding number of classes into which the
data are to be grouped
• This is done with a simple formula.
K = 1 + 3.3Log N
• Where K is Number of classes and N is the
Total Number of observations.
6. • In this example, the classes were found using
this formula.
K= 1 + 3.3 Log (27)
K= 5.7
• Rounding that off to the next whole number
got the number of classes. Which is 6.
• Therefore Number of Classes = 6
7. 2. Determine the range of variation
• “This is the difference between the largest
and the smallest value in the data.”
4- Largest value
1.85- Smallest value
So, Range= 4 - 1.85
Range = 2.15
8. 3. Class width determination
• Determining the approximate width of the classes can be
done by dividing the Range by Number of Classes.
Range- 2.15, Number of Classes- 6
Class width(Approximate) = 2.15/6
= 0.35
The approximate class width therefore used is 0.35
9. 4. Location of class limit
• The largest value in the data is 4, and therefore that is the upper limit of
the last class in the data. The class width can then be subtracted from
each limit until the minimum value is accommodated in the first class.
The classes are made like this:
4- 0.35 = 3.65
» 3.65- Becomes the lower limit
» 4- Is the upper limit
10. • The next class is calculated by:
3.64-0.35= 3.29
» 3.64- Upper limit
» 3.29- Lower limit
• The next class is calculated by:
3.28-0.35 = 2.93
» 3.28- Upper limit
» 2.93 Lower limit
11. • This process is continued until the last class is
made.
2.20-0.35 = 1.85
» 2.20- Upper Limit
» 1.85- Lower Limit
Notes: Classes- Also known as class limits, are the numbers or values of the variables which describe the classes. The smaller number is the lower class limit and the larger number is the larger class limit.
Class Boundaries- Are the precise numbers that separate one class from another. It is located midway between the upper limit of a class and the lower limit of the next higher class. E.g.
1.85- Lower limit of class
Class boundary will be- 1.85 + 1.84 / 2 = 1.845
However the upper limit boundary will be calculated like this.
2.20- Upper limit of class
Class boundary = 2.20+ 2.21/ 2
= 2.205
X – X represents the midpoint of the class. It is also known as the class mark or class midpoint. This value is calculated my adding the upper and lower limit of the class and dividing that value by two.
E.g.
3.29- Lower limit of class
3.64- Upper limit of class
Class midpoint = 3.29+3.64 / 2
=3.465
Frequency- The amount of observations whose values lies in each class. It represents all those observations that lie in the respected class limits
Tally- Another method used to count the number of observations that lie in the class limits. Each bar represents one observation.