Download Whitson PPT Chapter 2

Basic Assessment
Principles
Chapter 2
Measurement Scales

Nominal

Ordinal

Interval

Ratio
Criterion-Referenced
Instruments


Designed to compare an individual’s
performance to a stated criterion or
standard.
How was standard determined?



common practice
professional organizations or experts
empirically-determined
Norm-Referenced
Instruments


Interpretation of performance is based on the
comparison of an individual’s performance with
that of a specified group of people.
Evaluating the norming group
 size
 sampling
 representation
Sample Scores
Robert
Alice
Beth
Amy
Porter
72 Miles 96 Jason 68
82 Paul 59 Pedro 86
94 John 82 Kelly 92
77 Kevin 85 Justin 72
62 Ling 98 Sherry 67
Whitney 79
Jane
85
Michael
81
Rebecca 88
Maria
86
Frequency Distribution
X
f
50-59 60-69
1
3
70-79 80-89 90-100
4
8
4
Frequency Polygon
9
8
7
6
5
4
3
2
1
0
50-59
60-69
70-79
80-89
90-100
Frequency Histogram
8
7
6
5
4
3
2
1
0
60-69
70-79
80-89
90-100
Measures of Central
Tendency
Sample scores = 98, 98, 97, 50, 49

Mode (98)

Median (97)

Mean (78.4)
X

M 
N
Measures of Variability

Range

Variance

Standard Deviation
s
 X  M 
N
2
Normal Distribution
Skewed Distribution
mode
POSITIVE
mode
median
mean
NEGATIVE
median
mean
Types of Scores

Raw Scores

Percentiles or Percentile Ranks

Standard Scores




z scores
T scores
Stanines
age/grade-equivalent
Percentiles
X
50
60
70
80
90
f
1
3
4
9
4
%
5%
14%
19%
43%
19%
%ile
5
19
38
81
99*
Interpreting Percentiles

98th Percentile


98% of the group had a score at or below
this individual’s score
32nd Percentile


32% of the group had a score at or below
this individual’s score
If there were 100 people in the room, 32 of
them would have a score at or below this
individual’s score.
z Scores

z score =

Mean = 0

Standard deviation = 1
X-M
s
T Scores

Mean =50

Standard deviation = 10
Stanines
Stanines
1
2
3
4
5
6
7
8
9
Percentiles
1-4
5-11
12-23
24-40
41-59
60-76
77-88
89-95
96-99
% Individuals
4%
7%
12%
17%
20%
17%
12%
7%
4%
Standard scores
Additional Converted
Scores

Possible problematic scores

Age Norms or Age-Equivalent Norms

Grade Norms or Grade-Equivalent Norms
Evaluating the Norming
Group

Adequacy of norming group depends on:





Clients being assessed
Purpose for assessment
Way information will be used
Examine methods used for selecting
group
Examine characteristics of norming group
Sampling Methods

Simple random sample

Stratified sample

Cluster sample