9. Weighted mean and Percentile.notebook
March 27, 2014
Stascal Measures
To find the position of a score with a specific percentile:
• if n x p is a whole number, the position is the mean of n x p and (n x p) +1
• If n x p is a decimal, round up to find the position of the score.
Stascal Measures
Percentile and Percentile Rank
• Percentile: a number between 1 and 99 indicating the percent of the population with a score less than or equal to a specific value
• Percentile rank: the percent of the population with a score less than a specific score
Ex. The table give scores for a project, ranked lowest to highest.
a) determine the percentile rank for each
i) 14
ii) 11
b) which score is in each percentile?
i) 75th
Calculating percentile rank:
ii) 95th
SCORE
5
8
9
11
11
11
13
14
16
17
18
19
RANK
12
11
10
9
8
7
6
5
4
3
2
1
1. sort the scores from least to greatest
2. use the formula: p ­ percentile rank
L ­ number of scores less than the particular score
E ­ number of scores equal to itself
n ­ total number of scores
*Percentile ranks are usually rounded to the nearest whole number. Oct 2­7:23 AM
Oct 2­7:23 AM
Stascal Measures
Weighted Mean
• a mean in which each component has a different weighting factor
• to calculate a weighted mean, 1. convert any scores to decimals
Homework
p. #2,4,8 (Just for Foster) 2. multiply each score by its weight factor 3. add all values Ex.
Calculate the overall percent for the following student
weight factor
category
quiz
quiz 1 (15%)
assignment (15%)
mark
(out of 30)
in­class assignment
decimal X weight factor
40
(out of 60)
test
unit test
(25%)
(out of 120)
ISU independent study (15%)
decimal
24
89
43
(out of 60)
final exam exam (30%)
(out of 90)
72
Oct 2­7:23 AM
Mar 26­1:35 PM
Mar 26­2:00 PM
1