Download Basic Assessment Principles

Basic Assessment
Principles
Chapter 2
Measurement Scales
 Nominal
 Ordinal
 Interval
 Ratio
Norm-Referenced Instruments
 Individual’s score is compared to performance of
others who have taken the same instrument (norming
group)
 Example: personality inventory
 Evaluating the norming group
 size
 sampling
 representation
Criterion-Referenced Instruments
 Individual’s performance is compared to specific
criterion or standard
 Example: third-grade spelling test
 How are standards determined?
 common practice
 professional organizations or experts
 empirically-determined
Norm-Referenced: Sample Scores
Robert 72
Alice 82
Beth 94
Amy
77
Porter 62
Miles
Paul
John
Kevin
Ling
96
59
82
85
98
Jason 68 Whitney 79
Pedro 86 Jane
85
Kelly 92 Michael 81
Justin 72 Rebecca 88
Sherry 67 Maria
86
Frequency Distribution
X
f
50-59 60-69
1
3
70-79
4
80-89 90-100
8
4
Frequency Polygon
9
8
7
6
5
4
3
2
1
0
50-59
60-69
70-79
80-89
90-100
Histogram
8
7
6
5
4
3
2
1
0
60-69
70-79
80-89
90-100
Measures of Central Tendency
 Mode – most frequent score
 Median – evenly divides scores into two halves (50%
of scores fall above, 50% fall below)
 Mean – arithmetic average of the scores
X

 Formula: M 
N
Measures of Central Tendency
Example:
Sample scores – 98, 98, 97, 50, 49
 Mode = 98
 Median = 97
 Mean = 78.4
Measures of Variability
 Range – highest score minus lowest score
 Variance – sum of squared deviations from the mean
 Standard Deviation – square root of variance
 Formula: s 
 X  M 
N
2
Normal Distribution
Skewed Distribution
Types of Scores
 Raw scores
 Percentile scores/Percentile ranks
 Standard scores




z scores
T scores
Stanines
Age/grade-equivalent scores
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 taking the assessment, 32 of
them would have a score at or below this individual’s
score
Interpreting Percentiles
 Units are not equal
 Useful for providing information about relative
position in normative sample
 Not useful for indicating amount of difference
between scores
Types of Standard Scores
z Scores
 z score = X-M
s
 Mean = 0
 Standard deviation = 1
T Scores
 Mean = 50
 Standard deviation = 10
Stanines
Standard Scores: Summary
Additional Converted Scores
 Possible problematic scores
 Age-equivalent scores
 Grade-equivalent scores
 Problematic because:
 These scores do not reflect precise performance on an instrument
 Learning does not always occur in equal developmental levels
 Instruments vary in scoring
Evaluating the Norming Group
 Adequacy of norming group depends on:
 Clients being assessed
 Purpose of the assessment
 How information will be used
 Examine methods used for selecting group
 Examine characteristics of norming group
Sampling Methods
 Methods for selecting norming group:
 Simple random sample
 Stratified sample
 Cluster sample
Norming Group Characteristics





Size
Gender
Race/ethnicity
Educational background
Socioeconomic status
 Is the norming group appropriate for use with this
client?