Stat 104 – Lecture 15
Quantitative Variables
• Discrete variables
– Bag O’ Chips
– Rake it in!TM
– Binomial
• Win points with Bag O’ Chips
• O+ blood type.
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Quantitative Variables
• Continuous variables
– Height
– Heart Rate
2
30
Percent
20
10
0
40
45
50
55
60
65
70
75
80
Height
3
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Stat 104 – Lecture 15
Describe the sample
• Shape is symmetric and mounded
in the middle.
• Centered at 60 inches.
• Spread between 45 and 75 inches.
• 30% of the sample is between 60
and 65 inches.
4
Normal Models
• Our conceptualization of what the
distribution of an entire population of
values would look like.
• Characterized by a bell shaped curve
with population parameters
– Population mean = µ
– Population standard deviation = σ.
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Sample Data
0.08
0.07
Density
0.06
0.05
0.04
0.03
0.02
0.01
0.00
40
45
50
55
60
65
70
75
80
Height
6
2
Stat 104 – Lecture 15
Normal Model
0.08
0.07
Density
0.06
0.05
σ
0.04
0.03
0.02
0.01
0.00
40
45
50
55
µ60
65
70
75
80
Height (inches)
7
Normal Model
• Height
• Center:
– Mean, µ = 60 in.
• Spread:
– Standard deviation, σ = 6 in.
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68-95-99.7 Rule
• 68% of the values fall within 1
standard deviation of the mean.
• 95% of the values fall within 2
standard deviations of the mean.
• 99.7% of the values fall within 3
standard deviations of the mean.
9
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