Max’s 2 – year checkup

Weight 8o th percentile (also written as P 80 ) Length 90 th percentile (or P 90 ) Head Girth 85 th percentile (or P 85 ) What does that even mean, Dad?

Weights of 100 randomly selected 2 year old white American males (in pounds)

Weights of 100 randomly selected 2 year old white American males (in pounds)

Tell me everything you can about the weights of these 2 – year olds...

So...what’s with Max’s “80 th Percentile”?

How many of these 2 – year olds weigh less than 26 pounds?

How many of these 2 – year olds weigh less than 29 pounds?

How many of these 2 – year olds weigh less than 31 pounds?

So, Max is in the 80 th 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...

...or an ogive.

An ogive you might see one day (or maybe already have!)