Percentile RankPercentile Rank

Percentile rank (PR) refers to the position Percentile rank (PR) refers to the position within a group that a person with a particular within a group that a person with a particular score is at.score is at.

A person with percentile rank of 70 (Pr 70), A person with percentile rank of 70 (Pr 70), means that he /she scored the means that he /she scored the same as or same as or better than better than 70 percent of the group. 70 percent of the group.

Pr 50 Pr 50 means person scored means person scored same or same or better than better than 50 percent of group.50 percent of group.

Percentile Rank Percentile Rank – data on handout – data on handout

answers the questionanswers the question

What percentile rank tells us is What percentile rank tells us is within this group what position within this group what position a baby’s weight represents.a baby’s weight represents.

8 lbs 8 lbs For example ?For example ?And gives us some idea if this And gives us some idea if this

is high or low relative to groupis high or low relative to group

Percentile Rank - data on handoutPercentile Rank - data on handoutbirth weightsbirth weights

Step One – list the weights (or scores)Step One – list the weights (or scores)

Score(Weight)

Frequency CumulativeFrequency

Relative FreqPercent

10

9

8

7

6

5

4

Percentile Rank - data on handoutPercentile Rank - data on handoutbirth weights (birth weights (3030 babies) babies)

Step Two – Step Two – how many births (or how many births (or scoresscores) at each ) at each weightweight

Score(Weight)

FrequencyNumber of babies

10 2 babies weigh 10 lbs

9 2 babies weigh 9 lbs

8 5 babies weigh 8 lbs

7 10 babies weigh 7 lbs

6 7 babies weigh 6 lbs

5 3 babies weigh 5 lbs

4 1 babies weigh 4 lbs

Percentile Rank – Percentile Rank – Relative Frequency PercentRelative Frequency Percent

Step ThreeStep Three – – calculate what the calculate what the number at each score represents number at each score represents of the wholeof the whole

If 5 out of the 30 weigh 8 lbsIf 5 out of the 30 weigh 8 lbs, , what what does that weight represent as a does that weight represent as a percentage of the whole (30) ?percentage of the whole (30) ?

Percentile Rank - data on handoutPercentile Rank - data on handoutbirth weights (birth weights (3030 babies) babies)

Step Three – Step Three – relative frequency percentrelative frequency percent

Score(Weight)

FrequencyNumber of babies

Relative Frequency Percent

10 2 6.6 (7)

9 2 6.6 (7)

8 5 babies weigh 8 lbs 17.9 (18)

7 10 33.3 (33)

6 7 23.3 (23)

5 3 10.0 (10)

4 1 3.3 (3)

Percentile Rank - data on handoutPercentile Rank - data on handoutbirth weights (birth weights (3030 babies) babies)

Step Four – cumulative percent (Percentile Step Four – cumulative percent (Percentile Rank)Rank)

Score(Weight)

FrequencyNumber of babies

Relative Frequency Percent

Cumulative percent

PercentileRank

10 2 6.6 (7) 100 (has to be 100)

9 2 6.6 (7) 94

8 5 babies weigh 8

lbs*17.9 (18) 87 (Pr87) *

7 10 33.3 (33) 69

6 7 23.3 (23) 36

5 3 10.0 (10) 13

4 1 3.3 (3) 3

Percentile RankPercentile Rank A baby weighing 8 lbs amongst this group A baby weighing 8 lbs amongst this group

(births in a week in Pleasantville) would be(births in a week in Pleasantville) would be

Pr87 Pr87 (at the 87(at the 87thth percentile) percentile)

Which is Which is the same (weight) as, or the same (weight) as, or better than 87 % of the group better than 87 % of the group (babies born that week).(babies born that week).