VALIDITY AND RELIABILITY

VALIDITY OF A TEST

 

Validity – (Airasian, 2000) is concerned whether the information obtained from an assessment permits the teacher to make a correct decision about a student’s learning.

Types of Validity:

1.   Content Validity – refers to the relationship between a test and the instructional objectives, establishes content so that the test measures what it is supposed to measure.

2.   Criterion-related Validity – refers to the extent to which scores from a test relate to theoretically similar measures.

a.   Concurrent Validity – the criterion and the predictor data are collected at the same time.

b.   Predictive Validity – refers to a measure of the extent to which a student’s current test result can be used to estimate accurately the outcome of the student’s performance at a later time.

3.   Construct Validity – refers to the measure of the extent to which a test measures theoretical and unobservable variable qualities such as intelligence, math achievement, performance anxiety, and the like, over a period of time on the basis of gathering evidence.

a.   Convergent Validity – is a type of construct validation wherein a test has a high correlation with another test that measures the same construct.

b.   Divergent Validity – is a typeof construct validationwherein a test has low correlation with a test that measures a different construct.

c.    Factor Analysis – is another method of assessing the construct validity of a test using complex statistical procedures conducted with different procedures.

Important things to remember about Validity:

1.      Validity refers to the decisions we make, and not to the test itself or to the measurement.

2.     Like reliability, validity is not an all-or-nothing concept; it is never totally absent or absolutely perfect.

3.     A validity estimate, called a validity coefficient, refers to specific type of validity. It ranges between 0 to 1.

4.     Validity can never be finally determined; it is specific to each administration of the test.

Factors affecting the Validity of a Test Item:

1.   The test itself.

2.   The administration and scoring of a test.

3.   Personal factors influencing how students response to the test.

4.   Validity is always specific to a particular group.

Reasons that reduce the Validity of the Test Item:

1.   Poorly constructed test items.

2.   Unclear directions.

3.   Ambiguous test items.

4.   Too difficult vocabulary.

5.   Complicated syntax.

6.   Inadequate time limit.

7.   Inappropriate level of difficult.

8.   Unintended clues.

9.   Improper arrangement of test items.

Guide Questions to Improve Validity:

1.   What is the purpose of the test?

2.   How well the instructional objectives selected for the test do represents the instructional goals?

3.   Which test item format will be the best measure achievement of each objective?

4.   How many test items will be required to measure the performance adequately to each objective?

5.   When and how will the test be administered?

Validity Coefficient – is the computed value for the r_xy.

Coefficient of determination – indicates how much variation in the criterion can be counted for by the predictor (teacher test).

Example:

Interpretation:

          The correlation coefficient is 0.94, which means that the validity of the test is high, or 88.36% of the variance in the student’s performance can be attributed to the test.

RELIABILITY of a TEST

Reliability – refers to the consistency with which it yields the same rank for individual who takes the test more than once (Kubiszyn and Borich, 2007).

Factors Affecting Reliability of a Test:

1.   Length of the test.

2.   Moderate item difficulty.

3.   Objective scoring.

4.   Heterogeneity of the student group.

5.   Limited time.

Four Methods of Establishing Reliability of a Test:

1.   Test-retest Method – a type of reliability determined by administering the same test twice to the same group of students with any time interval between the tests.

FORMULA:

R_xy=     (n) (Σxy) –(Σx)(Σy)

              √ [(n)( Σx²) - (Σx)²] [(n)(Σy²) – (Σy)²]

2.   Equivalent Form – a type of reliability determined by administering two different but equivalent forms of the test to the same group of students in close succession.

3.   Split-half Method – administer test once and score two equivalent halves of the test.

4.   Kuder-Richardson Formula –administer the test once. Score the total test and apply the Kuder-Richardson formula.

Reliability Coefficient – is a measure f the amount of error associated with the test scores.

Description of reliability Coefficient:

a.   The range of the reliability coefficient is from 0-10.

b.   The acceptable range value is 0.60 or higher.

c.    The higher the value of the reliability coefficient, the more reliable the overall test scores.

d.   Higher reliability indicates that the test items measure the same thing.

Interpreting reliability coefficient

1.    The group variability will affect the size of the reliability coefficient.

2.   Scoring reliability limits the test score reliability.

3.   Test length affects test score reliability. As the length increases, the test’s reliability tends to go up.

4.   Item difficulty affects test score reliability. As test items become very easy or very hard, the test’s reliability goes down.

Level of Reliability Coefficient:

Example solving:

students	FT (x)	ST (y)	xy	X2	Y2
1	36	38	1368	1296	1444
2	26	34	884	676	1156
3	38	38	1444	1444	1444
4	15	27	405	225	729
5	17	25	425	289	625
6	28	26	728	784	676
7	32	35	1120	1024	1225
8	35	36	1260	1225	1296
9	12	19	228	144	361
10	35	38	1330	1225	1444
N=10	∑x=274	∑y=316	∑xy=9192	∑ X2=8332	∑ Y2=10400

 

   

Analysis:

          The reliability coefficient using the Pearson r = 0.76 means that it has  a high reliability. The scores of the 10 students conducted twice with one-week interval are consistent. Hence, the test has a high reliability.

REFLECTION:

          A good Tester is the one who prepares a "Test Plan" for every level of testing, and clearly describes its objectives & most important aspect is that he/she operates on it.

          A valid assessment is one that measures what it claims to measure, and is therefore predominantly concerned with accuracy. If the information provided are irrelevant to the learning objectives, it makes the interpretation of the test result invalid. In administering the test, the content must be in accordance to the learning objectives of the lesson.

          A reliable score is one that will give you the same/close score every time you do a test. It refers to the consistency which yields the same result as the test given for the second time. We can say that a test is effective and reliable when it can predict that the same test will come up with the same result.

         Both precision and accuracy are crucial in interpreting a score. To be effective in making the test, a teacher must know how to make it valid and reliable.