Max’s 2 – year checkup. Weight 8o th percentile (also written as P 80 ) Length 90 th percentile...
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Transcript of Max’s 2 – year checkup. Weight 8o th percentile (also written as P 80 ) Length 90 th percentile...
Weight8oth percentile (also written as P80)
Length90th percentile (or P90) Head Girth85th percentile (or P85)
What does that even mean, Dad?
Weights of 100 randomly selected 2 year old white American males (in pounds)
24 31 29 29 25 27 28 27 26 2526 29 31 26 29 30 29 29 20 2820 21 27 31 30 28 29 33 31 2927 28 29 28 31 28 31 27 29 3129 25 27 30 29 30 27 24 29 2826 26 30 31 29 30 29 29 23 3031 29 30 22 24 25 27 30 26 2425 29 28 31 25 22 27 28 26 2627 31 29 20 23 28 25 22 24 2425 31 24 31 31 25 27 28 28 29
Weights of 100 randomly selected 2 year old white American males (in pounds)
20 21 22 23 24 25 26 27 28 29 30 31 32 330
4
8
12
16
Weight (pounds)
Number of Boys
Tell me everything you can aboutthe weights of these 2 – year olds...
20 21 22 23 24 25 26 27 28 29 30 31 32 330
4
8
12
16
Weight (pounds)
Number of Boys
How many of these 2 – year olds weigh less than 26 pounds?
20 21 22 23 24 25 26 27 28 29 30 31 32 330
4
8
12
16
Weight (pounds)
Number of Boys
How many of these 2 – year olds weigh less than 29 pounds?
20 21 22 23 24 25 26 27 28 29 30 31 32 330
4
8
12
16
Weight (pounds)
Number of Boys
How many of these 2 – year olds weigh less than 31 pounds?
20 21 22 23 24 25 26 27 28 29 30 31 32 330
4
8
12
16
Weight (pounds)
Number of Boys
So, Max is in the 80th percentile for his weight, because, at 31 pounds, he weighs
more than 80% of 2 – year old boys.
In general, a percentile (or percentile rank) is the proportion of data that a
given point exceeds.
However...
It might be easier to see the percentiles with the a cumulative frequency histogram...
20 21 22 23 24 25 26 27 28 29 30 31 32 330
10
20
30
40
50
60
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80
90
100
Weight (pounds)
Number of Boys at or
below that weight
...or an ogive.
20 21 22 23 24 25 26 27 28 29 30 31 32 330
10
20
30
40
50
60
70
80
90
100
Weight (pounds)
Number of Boys at or
below that weight