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The pth %tile of a variable is given by
X(p) = m + ks
where k is a constant for the percentile concerned
¡@
|
Percentile |
K1 |
Central Percent Covered |
K2=2K1 |
|
30 |
70 |
0.524 |
40 |
1.048 |
|
25 |
75 |
0.674 |
50 |
1.348 |
|
20 |
80 |
0.842 |
60 |
1.684 |
|
15 |
85 |
1.036 |
70 |
2.072 |
|
10 |
90 |
1.282 |
80 |
2.564 |
|
5 |
95 |
1.645 |
90 |
3.29 |
|
2.5 |
97.5 |
1.96 |
95 |
3.92 |
|
1 |
99 |
2.326 |
98 |
4.652 |
|
0.5 |
99.5 |
2.576 |
99 |
5.152 |
Example 1:
To find the 95th percentile for mean = 35.1
and std dev = 1.5 in
-
K1=1.645
-
1.5*1.645=2.5 in
-
35.1+2.5=37.6 in
Example 2:
To find the adjustment needed for the
middle 90% of the same group
-
Range of adjustment: 1.5 x 3.29 = 4.9
in
-
Minimum (5th) : 35.1 - 2.5 = 32.6 in
-
Maximum (9th) : 35.1 + 2.5 = 37.6 in
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