Compare the following heights in inches: Boys Girls 72 61 74 64 70 65 68 66 69 68 70 67 68 65 69 63 67 62 70 65 71 66 67 64
Jan 18, 2016
Compare the following heights in
inches:
Boys Girls
72 61
74 64
70 65
68 66
69 68
70 67
68 65
69 63
67 62
70 65
71 66
67
64
66
Computational Computational Formulas and IQR’sFormulas and IQR’s
Computational Computational Formulas and IQR’sFormulas and IQR’s
Computational Formula:
22
2
1
xx
nsn
This is an easier computational formula that contains no rounding.
Let’s try it!
7
18
22
34
42
x
You try one!
4
8
12
18
22
34
38
x
Is the standard deviation affected by
outliers?
5
7
5
8
9
5
7
5
8
29
The standard deviation is sensitive to extreme
values.
67
65
68
70
74
60
61
64
67
68
The following data represents the heights of some students in my class.
a. Find the mean & st. dev.
b. What % are within 1 st. dev. Of the mean?
c. What % are within 2 st. dev. Of the mean?
IQR – Interquartile Range
• This is the measure of variability that is not affected by outliers.
• It’s based on quartiles.
25%25% 25%
25%
1Q 2Q 3Q
1Q
2Q
- This is the median of the lower ½ of the sample.
3Q
- This is the median.
- This is the median of the upper ½ of the sample.
3 1IQR Q Q
18 24 25 27 27 29 30 33 34
Find IQR
12 13 16 18 22 24 27 40
Find IQR
8 10 11 14 16 20 22 26 28 32
Find IQR
4 5 6 6 7 10 22
If normal distribution – then you can estimate the
standard deviation with the IQR.
1.35
IQRStandard
Deviation
*Can also be use to check to see if a distribution is normal – if much larger then it’s skewed.
Homework• Worksheet
• Use the new formula to compute the standard deviation.
Now for the Lab!