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Stat 101: Lecture 8
Measures of Spread
• Based on the deviation from the
sample mean.
• Deviation
(y − y)
1
9-hole Golf Scores
46, 44, 50, 43, 47, 52
282
y=
= 47 strokes
6
40
45
50
55
2
Deviations
–4
–3
–1
40
45
+5
+3
50
55
3
Stat 101: Lecture 8
Sample Variance
Almost the average squared deviation
(
(y − y) )
∑
=
2
s
2
n −1
4
Sample Variance
s2 =
(16 + 9 + 1 + 25 + 9 ) = 60
5
= 12 strokes 2
5
5
Sample Standard Deviation
(∑ ( y − y ) )
2
s=
s =
s=
12 = 3 . 46 strokes
2
n −1
6
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