Frequency Distribution
Steps in Organizing Data
 Arrange data into an array
 Decide on number of classes (k)
 Determine class interval (CI)
 Prepare tally sheet
Frequency Distribution
 Data set:

81 86 82 76 92 89 87 82 88 83 85 91
77 93 83 98 92 87 87 82 71 88 78 84
89 93 86 99 85 87 73 90 79 89 83
Frequency Distribution
 Arrange data into an array
71 81 83
87 89
92 73 82 84 87
76 82 85 87 89
93 77 82 85 87
90 98
78 83 86
88 91 99 79 83
86
92
88
Frequency Distribution
Decide on number of classes (k)
 Use Sturges' Rule
k = 1 + 3.3 log n
k = 1 + 3.3 log n
= 1 + 3.3 log 35
= 1 + 3.3 (1.544) = 6.095 ≈6
Frequency Distribution
 Determine class interval (CI)
•Use the formula
CI = HV − LV
k
CI =( HV − LV)/ k = (99 − 71)/ 6 = 28/ 6 ≈5
Frequency Distribution
Class
Tally
Frequency
70-74
II
2
75-79
IIII
4
80-84
IIIII-III
8
85-89
IIIII-IIIII-III
13
90-94
IIIII-I
6
95-99
II
2
Frequency Distribution
 Here are some test scores from a math class.
65 91
85
76
85
87
79
93
82 75
100
70
88
78
83
59
87 69
89
54
74
89
83
80
94 67
77
92
82
70
94
84
96 98
46
70
90
96
88
72
Frequency Distribution
Class Frequency Relative Frequency
Percent
41-50
1
1/40
2.5%
51-60
2
2/40
5%
61-70
6
6/40
15%
71-80
8
8/40
20%
81-90
14
14/40
35%
91-100
9
9/40
22.5%
Frequency Distribution
Class
Frequency
Cumulative (Less Than)
41-50
1
1
51-60
2
3
61-70
6
9
71-80
8
17
81-90
14
31
91-100
9
40
Frequency Distribution
Class
Frequency
Cumulative (Greater Than)
41-50
1
40
51-60
2
39
61-70
6
37
71-80
8
31
81-90
14
23
91-100
9
9
Frequency Distribution
 Let’s suppose that you are collecting data on how
many hours of sleep college students get each night.
After conducting a survey of 30 of your classmates,
you are left with the following set of scores:
7, 5, 8, 9, 4, 10, 7, 9, 9, 6, 5, 11, 6, 5, 9, 10, 8, 6,
9, 7, 9, 8, 4, 7, 8, 7, 6, 10, 4, 8