Lesson 1
Author: Atul Roy
Remember to read the definitions of
Numerical or Quantita
t
ive Data
Categorical or Qualitative data
Descriptive Statistics
Inferential Statistics
Distribution of the data
Topic 1.
Organization and Display of Numerical Data
Example 1.
The following data shows the prices of the townhomes on Truffle Lane in
Montgomery County, Maryland. The data is obtained from the real property
search data base of the State of Maryland.
The townhomes were built and sold in the year 20002001 and the prices are the
initial purchase prices of the homes. Since all the houses were over $200,000
the list shows only the amount that was paid in excess of $200,000 rounded to
the nearest thousandth.
price paid (over $200,000)
67
25
38
36
31
24
45
72
30
5
13
1
2
63
53
21
5
77
34
16
15
39
45
19
23
23
12
31
25
12
23
33
58
T
hat is the number 67 means that the house was sold for $267,000 (rounded.)
One way to organize and display such
data is called Stem and Leaf Diagram
Since an ordered Stem and Leaf Diagram is more meaningful, let us first put the
data in order
1
2
5
5
12
12
13
15
16
19
21
23
23
23
24
25
25
30
31
31
33
34
36
38
39
45
45
53
58
63
67
72
77
Treating all the numbers as two digit numbers, that is 1 as 01 etc., we may use
the first digit as stem and the second digit as leaf and the display will be
1
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0*1255
1*223569
2*1333455
3*01134689
4*55
5*38
6*37
7*27
Note that a stemplot will give an idea of the shape of a distribution. It will help
you visually locate the outliers (we shall see a well formulated approach to
outliers in the
lesson
2.)
It helps us locate the vital numbers, for example
0*1255
1*223569
2*133345
5
3*01134689
4*55
5*38
6*37
7*27
you may see that 25 is in the center of the distribution in the sense that it is
right in the middle, telling us that half of the homes were sold at 225,000 or
below.
Such a value is called the median of the data, we shall take median up more in
detail in the
lesson
2.
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 Fall '08
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 Statistics, Inferential Statistics, Frequency, Frequency distribution, Histogram, Summary statistics

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