1. CHAPTER 5 Test Scores as Composites
This Chapter is about the Quality of Items in a Test.

2. Test Scores as Composites
What is the Composite Test Score?
A composite test score is a total test score created by summing two or more subtest scores i.e., WAIS IV Full Scale IQ consisted of 1-Verbal Comprehension Index, 2-Perceptual Reasoning Index, 3-Working Memory Index, and 4-Processing Speed Index. Qualifying Examinations and EPPP Exams are also composite test scores.

3. Item Scoring Schemes [skeems]Systems We have 2 different scoring system
1. Dichotomous Scores
Dichotomous Scores are restricted to 0 and 1 such as scores on True and False, and multiple-choice question
2. Non-dichotomous Scores
Non dichotomous Scores are not restricted to 0 and 1
Can have range of possible points such as in essays. 1,2, 3, 4, 5……..

4. Dichotomous Scheme Examples
1. The space between nerve cell endings is called the
a. Dendrite
b. Axon ;
c. Synapse
d. Neutron
(In this item, responses a, b, and d are scored 0; response c is scored 1.)
2. Teachers in public school systems should have the right to strike.
a. Agree
b. Disagree
(In this item, a response of Agree is scored 1; Disagree is scored 0) .
Or, you can use True or False.

5. Practical Implication for Test Construction
Variance and Covariance measure the quality of items in a test.
Reliability and validity measure the quality of the entire test.
σ²=SS/N  used by one set of data
Variance is the degree of variability
of scores from mean.

6. Practical Implication for Test Construction
Correlation is based on a statistic called Covariance (Cov xy or S xy) COVxy=SP/N-1  used for 2 sets of data
Covariance is a number that reflects the degree to which 2 variables vary together.
r=sp/√ssx.ssy

7. Variance X σ² = ss/N Pop 1 s² = ss/n-1 or ss/df Sample 2 4 5
SS=Σx²-(Σx)²/N
SS=Σ( x-μ)²
Sum of Squared Deviation from Mean

8. Covariance
Covariance is a number that reflects the degree to which 2 variables vary together.
Original Data
X Y

9. Covariance COVxy=SP/N-1 2 ways to calculate the SP SP= Σxy-(Σx.Σy/N)
SP= Σ(x-μx)(y-μy)
SP requires 2 sets of data
SS requires only one set of data

10. Descriptive Statistics for Dichotomous Data

11. Descriptive Statistics for Dichotomous Data Item Variance & Covariance

12. Descriptive Statistics for Dichotomous Data
P=Item Difficulties:
P= (#of examinees who answered an item correctly / total # of examinees or P=f/N
See handout
The higher the P value The easier the item

13. Relationship between Item Difficulty P and σ²
Variance
σ² (quality)
0 difficult easy
P= Item Difficulty

14. Non-dichotomous Scores Examples
1. Write a grammatically correct German sentence using the first person singular form of the verb verstehen. (A maximum of 3 points may be awarded and partial credit may be given.)
2. An intellectually disabled person is a nonproductive member of society.
5. Strongly agree 4. Agree, 3. No opinion
2. Disagree 1. Strongly disagree
(Scores can range from 1 to 5 points. with high scores indicating a positive attitude toward intellectually disabled citizens.)

15. Descriptive Statistics for Non-dichotomous Variables

16. Descriptive Statistics for Non-dichotomous Variables

17. Variance of a Composite “σ²C”
σ²=SS/N
σ²a=SSa/Na σ²b=SSb/Nb
σ²C= σ²a+σ²b
Ex.
From WAIS III-- FSIQ=VIQ+PIQ
If More than 2 subtests, σ²C=σ²a+σ²b+σ²c… Calculate the variance for each subtest and add them up.

18. Variance of a Composite “σ²C”
What is the Composite Test Score?
Ex. WAIS IV Full Scale IQ which consist of a-Verbal Comprehension Index, b-Perceptual Reasoning Index, c-Working Memory Index, and
d-Processing Speed Index.
More than 2 subtests
σ²C=σ²a+σ²b+σ²c+σ²d

19. *Suggestions to Increase the Total Score Variance of a Test
1-Increase the number of items in a test
2-Item difficulties p (medium range)
3-Items with similar content have higher correlations & higher covariance
4-Item scores & total scores variances alone are not indices (in-də-ˌcēz) of test quality (reliability and validity).

20. *1-Increase the Number of Items in a Test (how to calculate the test variance)
Variance for a test of 25 items is higher than a variance for a test of 20 items.
σ²=N(σ²x)+N(N-1)(COVx)=
Ex. If the COVx=items covariance = (0.10)
σ²x=items variance  (0.20)
N= #of items in a test -- first try N=20
σ²=test variance  For 20 items 42 ,
then try N=25
and σ²=test variance for 25 items 65

21. 2-Item Difficulties
Item difficulties should be almost equal for all of the items and difficulty levels should be in the medium range.

22. 3-Items with Similar Content have Higher Correlations & Higher Covariance

23. 4- Item Scores & Total Scores Variances Alone are not Indices (in-də-ˌcēz) of Test Quality
Variance and Covariance are important and necessary however, they are not sufficient to determine the test quality.
To determine a higher level of test quality we use Reliability and Validity.

24. UNIT II RELIABILITY
CHAP 6: RELIABILITY AND THE CLASSICAL TRUE SCORE MODEL
CHAP 7: PROCEDURES FOR ESTIMATING RELIABILITY
CHAP 8: INTRODUCTION TO GENERALIZABILITY THEORY
CHAP 9: RELIABILITY COEFFICIENTS FOR CRITERION-REFERENCED TESTS

25. CHAPTER 6 Reliability and the Classical True Score Model
Reliability (p)=Reliability is a measure of consistency/dependability, or when a test measures same thing more than once and results in same outcome.
Reliability refers to the consistency of examinees performance over repeated administrations of the same test or parallel forms of the test (Linda Crocker Text).

26. THE MODERN MODELS

27. *TYPES OF RELIABILITY TYPE OF RELIABILITY WHT IT IS HOW DO YOU DO IT
WHAT THE RELIABILITY COEFFICIENT LOOKS LIKE
Test-Retest
2 Admin
A measure of stability
Administer the same test/measure at two different times to the same group of participants
r test1.test2
Ex. IQ test
Parallel/alternate Interitem/Equivalent Forms
A measure of equivalence
Administer two different forms of the same test to the same group of participants
r testA.testB
Ex. Stats Test
Test-Retest with Alternate Forms
A measure of stability and equivalence
On Monday, you administer form A to 1st half of the group and form B to the second half.
On Friday, you administer form B to 1st half of the group and form A to the 2nd half
Inter-Rater
1 Admin
A measure of agreement
Have two raters rate behaviors and then determine the amount of agreement between them
Percentage of agreement
Internal Consistency
A measure of how consistently each item measures the same underlying construct
Correlate performance on each item with overall performance across participants
Cronbach’s Alpha Method
Kuder-Richardson Method
Split Half Method
Hoyts Method

28. Test-Retest Class IQ Scores
Students X 1st time on MonY 2nd time on Fri
John Jo
Mary
Kathy
David

29. Parallel/alternate Forms
Scores on 2 forms of stats tests
Students Form A Form B
John Jo
Mary
Kathy
David

30. Test-Retest with Alternate Forms
On Monday, you administer form A to 1st half of the group and form B to the second half. On Friday, you administer form B to 1st half of the group and form A to the 2nd half
Students Form A to 1st group (Mon) Students Form B to 2nd group (Mon)
David Mark
Mary Jane
Jo George
John Mona
Kathy Maria
Next slide

31. Test-Retest with Alternate Forms
On Friday, you administer form B to 1st half of the group and form A to the second
Students Form B to 1st group (Fri) Students Form A to 2nd group (FRi)
David Mark
Mary Jane
Jo George
John Mona
Kathy Maria

32. HOW RELIABILITY IS MEASURED
Reliability is Measured by Using a
Correlation Coefficient
r test1•test2 or r x.y
Reliability Coefficients:
Indicates how scores on one test change, relative to scores on a second test
Can range from 0.0 to ±1
±1.00 = perfect reliability
0.00 = no reliability

33. THE CLASSICAL
MODEL

34. A CONCEPTUAL DEFINITION OF RELIABILITY CLASSICAL MODEL
Method Error
Observed Score = True Score ± Error Score
Trait Error
X=T±E

35. Classical Test Theory The Observed Score, X=T+E
X is the score you actually record or observe on a test.
The True Score, T=X-E or, the difference between the Observed score and Error score is the True score
T score is the reflection of the examinee true knowledge
The Error Score, E =X-T or, the difference between the Observed score and True score is the Error score.
E are factors that cause the True Score and observed score to differ.

36. A CONCEPTUAL DEFINITION OF RELIABILITY
Method Error
Observed Score = True Score ± Error Score
Trait Error
(X) Observed Score X=T±E
Score that actually observed
Consists of two components
True Score
Error Score

37. A CONCEPTUAL DEFINITION OF RELIABILITY
Method Error
Observed Score = True Score ± Error Score
Trait Error
True Score T=X-E
Perfect reflection of true value for individual
Theoretical score

38. A CONCEPTUAL DEFINITION OF RELIABILITY
Method Error
Observed Score = True Score ± Error Score
Trait Error
Method error is due to characteristics of the test or testing situation
Trait error is due to individual characteristics
Conceptually, Reliability =
True Score
Observed Score
Reliability of the observed score becomes higher if error is reduced!!
True Score
True Score + Error Score

39. A CONCEPTUAL DEFINITION OF RELIABILITY OR
Method Error
Observed Score = True Score ± Error Score
Trait Error
Error Score E=X-T
Is the Difference between Observed and True score ±
X=T±E
95=90+5 or 85=90-5 The difference between T and X is 5 points or E=±5

40. The Classical True Score Model
X=T±E
X= Represents the observed test score
T= Represents the individual's True knowledge of score
E= Represents the random error component

41. Classical Test Theory What Makes up the Error Score? E=X-T
Error Score consist of;
1-Method Error and 2-Trait Error
1-Method Error
Method Error is the difference between True & Observed Scores resulting from the test or testing situation.
2-Trait Error
Trait Error is the difference between True & Observed Scores resulting from the characteristics of examinees.
See next slide

42. What Makes up the Error Score?

43. Expected Value of True Score
Definition of the True Score
The True score is defined as the expected value of the examinees’ test scores (mean of observed scores) over many repeated testing with the same test.

44. Definition of the Error Score
Error scores for an examinee over many repeated testing should be Zero.
eEj=Tj-Tj=0
eEj=Expected value of Error
Tj=Examinee’ True Score
Ex. next

45. Error Score
X-E=T or, the difference between the Observed score and Error score is the True score (scores are from the same examinee)
98-8= 90
88+2=90
80+10=90
100-10= X±E=T
95-5=90
81+9=90
90-0=90 =0

46. *INCREASING THE RELIABILITY OF A TEST Meaning Decreasing Error 7 Steps
1. Increase Sample Size (n)
2. Eliminate Unclear Questions
3. Standardize Testing Conditions
4. Moderate the Degree of Difficulty of
the tests (P)
5. Minimize the Effects of External Events
6. Standardize Instructions (Directions)
7. Maintain Consistent Scoring Procedures (use rubric)

47. *Increasing Reliability of your Items in a Test

48. *Increasing Reliability Cont..

49. How Reliability (p) is Measured for an Item/score
P=True Score/True Score + Error Score or p=T/T+E
0=== p === ±1
Note: In this formula you always add your Error(the difference between T and X) to the True Score in the denominator (±) , Whether is positive or negative.
p=T/T + (the difference between T and X which is E)
p=T/T+E

50. Which Item has the Highest Reliability
Which Item has the Highest Reliability? Maximum points for this question is p=T/T+E
+2= 8……….. 8/10=0.80
-3=6…………. 6/9=0.666
+7=1……….…1/8=0.125
-1=9…………..9/10=0.90
+4=6………....6/10=0.60
-4=6……….....6/10=0.60
+1=7………....7/8=0.875
0=10…………10/10=1.0
-5=4…………..4/9=0.444
+6=3…………..3/9=0.333
>MORE ERROR <LESS RELIABLE

51. How Classical Reliability (p) is Measured for a Test
X=T+E
p=T/X…for an essay item/score
Examinees
1. X1=t1+e Ex. 10 = 7+3
2. X2=t2+e Ex. 8 =
3. X3=t3+e Ex. 6 =
Then calculate theσ²X=4 & σ²T=2.33

52. How Classical Reliability (p) is Measured for a Test
Reliability Coefficient for All Items
px1x2=σ²T/σ²X
Px1x2 for previous ex=2.33/4.00= 0.58
Pk=σ²T/σ²X

53. How Reliability Coefficient (p) is Measured for a Test
T X T±E=X
3+2= 5
4+3=7
8+6=13
9+5=14
2+1=3
1+1=2
8+1=9
7+3=10
P= σ²T/ σ²x /19.554= 0.493

54. Reliability Coefficient (p) for parallel test forms
Reliability Coefficient (p) =The correlation between scores on parallel test forms.
Next slide

55. X±E=T Scores on Parallel Test Forms
X Test A Y Test B
98-2= =89
88+2= =86
80+11= =83
100-8= =87
95-3= =85
81+12= =80
88+1= =83
90-3= =91
r=sp/√ssx.ssy r=0.882

56. *Reliability Coefficient and Reliability Index
Reliability Coefficient- px1x2=σ²T/σ²X
Reliability Index pxt=σT/σX
Therefore-px1x2=(pxt)²
Or pxt =
Just like the relationship between σ² and σ
The higher the item-reliability index,
The higher the internal consistency of the test.

57. *Reliability Coefficient and Reliability Index
PX1X2= σ²T/σ²X
Reliability Coefficient is the correlation coefficient that expresses the degree of reliability of a test.
Reliability Index
PXT= σT/σX
Reliability index is the correlation coefficient that expresses the degree of relationship between True (T) and Observed (X) scores of a test. It is the √ of Reliability Coefficient.

58. Reliability of a Composite C=a+b…..+k
Two Ways to Determine/predict the Reliability of the Composite Test Scores
*1-Spearman Brown Prophecy Formula
Allows us to estimate the reliability of a composite of parallel tests when the reliability of one of these tests is known.
Ex. Next
*2 -CRONBACH’S Alpha (α) or Coefficient (α)

59. *Next week Split Half Reliability Method which is the same as Spearman Brown Prophecy Formula when K=2

60. *1. Spearman Brown Prophecy Formula
*1. Spearman Brown Prophecy Formula

61. *1. Spearman Brown Prophecy Formula
*1. Spearman Brown Prophecy Formula

62. If N or K=2 then, we can call it Split half Reliability Method which is used for Measuring the Internal Consistency Reliability (see next chapter)
The effect of changing test length can also be estimated by using Spearman Brown Prophecy Formula. Just like increasing the variance of a test by increasing the # of items in a test (Chapter 5)

63. *The Spearman-Brown Prophcy Formula is used for: a,b,c
a. Correcting for one half of the test by estimating the reliability of the whole test.
b. Determining how many additional items are needed to increase reliability up to a certain level.
c. Determining how many items can be eliminated without reducing reliability below a predetermined level

64. Reliability of a Composite C=a+b…..+k
*2-CRONBACH’S Alpha (α) or Coefficient (α) is a preferred statistic
Allows us to estimate the reliability of a composite when we know the composite score variance and/or the covariance among all its components.
Next slide

65. Reliability of a Composite C=a+b…..+k
*2-CRONBACH’S Alpha (α) or Coefficient (α)
α=Pccʹ= (1-
K= # of tests=3
σ²i= Variance of each test σ²ta, σ²tb, σ²tc
σ²ta =2, σ²tb =3, σ²tc=4
σ²C= Composite score variance=12

66. The Standard Error of Measurement σE or σM
Standard Error of Measurement is the Mean of the Standard Deviations (σ) of all errors (E) made by several examinee.
E=T-X
Examinees Test Test 2 Test 3 Test 4
E=95-90=
E=85-86=
E=90-95=
E=95-93=
σ σ σ σ4

67. *The Standard Error of Measurement σE
1. Find the σs of these errors (E) for all of the examinees tests.
2. The mean/average for these σs is called the Standard Error of Measurement
σE = σx
Pxxʹ= r =reliability coefficient  or use Px1x2 for parallel tests.
σx=Standard Deviation for a Set of Observed Scores(X).

68. *The Standard Error of Measurement σE
is a tool used to estimate or infer how far an observed score (X) deviates from a true score (T).
σE = σx
Pxxʹ=r=reliability coefficient=use Px1x2 for parallel tests=.91
σx=Standard Deviation for a Set of Observed Scores=  σE=3 next slide

69. The Standard Error of Measurement σE
This means the average difference between the True scores (T) and Observed scores (X) is 3 points for all examinees which is called the Standard Error of Measurement.